a bright and vivid flash of fire, suddenly appearing in the atmosphere, and commonly disappearing in an instant, sometimes attended with clouds and thunder, and sometimes not.

The phenomena of lightning are always surprising, and sometimes very terrible; neither is there any kind of natural appearance in which there is more diversity, not two flashes being ever observed exactly similar to one another. In a serene sky, the lightning, in this country at least, almost always hath a kind of indistinct appearance without any determinate form, like the sudden illumination of the atmosphere occasioned by firing a quantity of loose gunpowder; but when accompanied with thunder, it is well defined, and hath very often a zig-zag form. Sometimes it makes only one angle, like the letter V, sometimes it hath several branches, and sometimes it appears like the arch of a circle. But the most formidable and destructive form which lightning is ever known to assume is that of balls of fire. The motion of these is very often easily perceptible to the eye; but wherever they fall, much mischief is occasioned by their bursting, which they always do with a sudden explosion like that of fire-arms. Sometimes they will quietly run along, or rest for a little upon any thing, and then break into several pieces, each of which will explode; or the whole ball will burst at once, and produce its mischievous effects only in one place. The next to this in its destructive effects is the zig-zag kind; for that which appears like indistinct flashes, whose form cannot be readily observed, is seldom or never known to do hurt.—The colour of the lightning also indicates in some measure its power to do mischief; the palest and brightest flashes being most destructive; such as are red, or of a darker colour, commonly doing less damage.

A very surprising property of lightning, the zig-zag kind especially when near, is its seeming omnipresence. If two persons are standing in a room looking different ways, and a loud clap of thunder accompanied with zig-zag lightning happens, they will both distinctly see the flash, not only by that distinct illumination of the atmosphere which is occasioned by fire of any kind; but the very form of the lightning itself, and every angle it makes in its course, will be as distinctly perceptible, as though they had looked directly at the cloud from whence it proceeded. If a person happened at that time to be looking on a book, or other object which he held in his hand, he would distinctly see the form of the lightning between him and the object at which he looked. This property seems peculiar to lightning, and to belong to no other kind of fire whatever.

The effects of lightning are generally confined within a small space; and are seldom similar to those which able effects accompany explosions of gun-powder, or of inflammable air in mines. Instances of this kind, however, have occurred; the following is one of the most remarkable of which we have any distinct account.

"August 2, 1763, about six in the evening, there arose at Anderlight, about a league from Brussels, a conflict of several winds borne upon a thick fog. This conflict lasted four or five minutes, and was attended with a frightful hissing noise, which could be compared to nothing but the yellings of an infinite number of wild beasts. The cloud then opening, discovered a kind of very bright lightning, and in an instant the roofs of one side of the houses were carried off and dispersed at a distance; above 1000 large trees were broke off, some near the ground, others near the top, some torn up by the roots; and many both of the branches and tops carried to the distance of 60, 100, or 120 paces; whole coppices were laid on one side, as corn is by ordinary winds. The glass of the windows which were most exposed was shivered to pieces. A tent in a gentleman's garden was carried to the distance of 4000 paces; and a branch torn from a large tree, struck a girl in the forehead as she was coming into town, at the distance of 40 paces from the trunk of the tree, and killed her on the spot."

These terrible effects seem to have been owing to the prodigious agitation in the air, occasioned by the emission of such a vast quantity of lightning at once; or perhaps to the agitation of the electric fluid itself, which is still more dangerous than any concussion of the atmosphere; for thunder-forms will sometimes produce most violent whirlwinds, such as are by the best philosophers attributed to electricity, nay, even occasion an agitation of the waters of the ocean itself; and all this too after the thunder and lightning had ceased.—Of this we have the following instances.

"Great Malvern, October 16, 1761. On Wednesday last, we had the most violent thunder ever known in the memory of man. At a quarter past four in the afternoon I was surprized with a most shocking and dismal noise; 100 forges (the nearest resemblance I can think of), were they all at work at once, could scarce equal it. I ran to the fore-door, and casting my eye upon the side of the hill about 400 yards to the south-west of my house, there appeared a prodigious smoke, attended with the same violent noise. I ran back into the house, and cried out, a volcano (for so I thought) had burst out of the hill; but I had no sooner got back again, than I found it had defended, and was passing on within about 100 yards of the south end of my house. It seemed to rise again in the meadow just below it; and Lightning continued its progress to the east, rising in the same manner for four different times, attended with the same dismal noise as at first; the air being filled with a nauseous and sulphureous smell. I saw it gradually decrease till quite extinguished in a turnip-field about a quarter of a mile below my house. The turnip leaves, with leaves of trees, dirt, sticks, &c., filled the air, and flew higher than any of these hills. The thunder ceased before this happened, and the air soon afterwards became calm and serene."—The vast column of smoke mentioned in the above letter was so large, that a physician of eminence at Worcester saw it in its progress down the hill, about a mile from Feckenham, which is above 20 miles from Malvern.—In August 1763, a most violent storm of thunder, rain, and hail, happened at London, which did damage in the adjacent country, to the amount of £50,000. Hailstones fell of an immense size, from two to ten inches circumference; but the most surprising circumstance was the sudden flux and reflux of the tide in Plymouth pool, exactly corresponding with the like agitation in the same place, at the time of the great earthquake at Lisbon.

Instances are also to be found, where lightning, by its own proper force, without any assistance from those less common agitations of the atmosphere or electric fluid, hath thrown stones of immense weight to considerable distances; torn up trees by the root, and broke them in pieces; shattered rocks; beat down houses, and set them on fire, &c.

A very singular effect of lightning is mentioned in the 66th volume of the Philosophical Transactions, upon a pyed bullock. It happened in the county of Sussex about the end of August 1774. The bullock was white and red; and the lightning stripped off the white hair leaving the red untouched. The following is a particular account of the matter. "In the evening of Sunday, the 28th of August, there was an appearance of a thunder-storm, but we heard no report. A gentleman who was riding near the marshes not far distant from this town (Lewes) saw two strong flashes of lightning, seemingly running along the ground of the marsh, at about nine o'clock in the evening. On Monday morning, when the servants of Mr. Roger, a farmer at Swanborough, in the parish of Iford, went into the marsh to fetch the oxen to their work, they found one of them, a four-year-old steer, standing up to appearance much burnt, and so weak as to be scarce able to walk. The animal seemed to have been struck by lightning in a very extraordinary manner. He is of a white and red colour; the white in large marks, beginning at the rump bone, and running in various directions along both the sides; the belly is all white, and the whole head and horus white likewise. The lightning, with which he must have been undoubtedly struck, fell upon the rump bone, which is white, and distributed itself along the sides in such a manner as to take off all the hair from the white marks as low as the bottom of the ribs, but so as to leave a lift of white hair, about half an inch broad, all round where it joined to the red, and not a single hair of the red appears to be touched. The whole belly is unhurt, but the end of the sheath of the penis has the hair taken off; it is also taken off from the dewlap; the horns and the curled hair on the forehead are uninjured; but the hair is taken off from the sides of the face, from the flat part of the jaw-bones, and from the front of the face in stripes. There are a few white marks on the side and neck, which are surrounded with red; and the hair is taken off from them, leaving half an inch of white adjoining to the red. The farmer anointed the ox with oil for a fortnight; the animal purged very much at first, and was greatly reduced in flesh, but is now recovering."

In another account of this accident, the author supposes that the bullock had been lying down at the time he was struck; which shows the reason that the under parts were not touched. "The lightning, conducted by the white hair, from the top of the back down the sides, came to the ground at the place where the white hair was left entire."

The author of this account says, that he inquired of a Mr. Tooth a farrier, whether he ever knew of a similar accident; and that he told him "the circumstance was not new to him; that he had seen a great many pyed bullocks struck by lightning in the same manner as this; that the texture of the skin under the white hair was always destroyed, though looking fair at first; but after a while it became sore, throwing out a putrid matter in pustules, like the small-pox with us, which in time falls off, when the hair grows again, and the bullocks receive no farther injury;" which was the case with the bullock in question. In a subsequent letter, however, the very same author informs us, that he had inquired of Mr. Tooth "whether he ever saw a stroke of lightning actually fall upon a pyed bullock, so as to destroy the white hair, and show evident marks of burning, leaving the red hair uninjured?" He said he never did; nor did he recollect any one that had. He gave an account, however, of a pyed horse, belonging to himself, which had been struck dead by lightning in the night-time." The explosion was so violent, that Mr. Tooth imagined his house had been struck, and therefore immediately got up. On going into the stable he found the horse almost dead to appearance, though it kept on its legs near half an hour before it expired. The horse was pyed white on the shoulder and greatest part of the head; viz., the forehead and nose, where the greatest force of the stroke came. "The hair was not burnt nor discoloured, only so loosened at the root, that it came off with the least touch. And this is the case, according to Mr. Tooth's observation, with all that he has seen or heard of; viz., the hair is never burnt, but the skin always affected as above mentioned. In the horse, all the blood in the veins under the white parts of the head was quite stagnated, though he could perceive it to flow in other parts as usual; and the skin, together with one side of the tongue, was parched and dried up to a greater degree than he had ever seen before."

Another instance is mentioned of this extraordinary effect of lightning upon a bullock, in which even the small red spots on the sides were unaffected; and in this, as well as the former, the white hair on the under part of the belly, and on the legs, was left untouched.

All these, however, are to be considered as the more unusual phenomena of lightning; its common mode of action being entirely similar to that of a charged Leyden vial, where the electric matter discharges itself. Lightning itself from a substance positively electrified to one that is negatively so. The indentity of electric matter and lightning seems now, indeed, so well established, that there is not the least foundation for seeking any other solution of the phenomena of lightning, than what may be obtained by comparing them with those of our electrical experiments. The different forms of the flashes are all exemplified in those of electrical sparks. Where the quantity of electricity is small, and consequently incapable of striking at any considerable distance, the spark appears straight, without any curvature or angular appearance; but where the electricity is very strong, and of consequence capable of striking an object at a pretty considerable distance, it assumes a crooked or zig-zag form. This is always the case with Mr Nairn's very powerful machines, the conductors of which are six feet in length and one foot in diameter. Sparks may be taken from them at the distance of 16, 17, or even 20 inches; and all of these put on the angular zig-zag form of lightning. The reason of this appearance, both in these sparks and in the lightning, is, that the more fluid electric matter hath to pass through the denser and less fluid atmosphere with great rapidity; and in fact, this is the way in which all the more fluid substances pass through those that are less so, at least when their velocity becomes considerable. If bubbles of air or steam pass very gently up through water, their course from the bottom to the top of the vessel will differ very little, if at all, from a straight line; but when they are impelled by a considerable force, as in air blown from a bellows, or the bubbles of steam which arise in boiling water, their course is then marked by waved and crooked lines, and the deflection of the bubbles to the right or left will be precisely in proportion to their ascending velocity, and to the weight of the water by which they are resisted.

In the case of air blown through water, however, or steam ascending from the bottom of a vessel of boiling water, though the course of the bubbles is waved and crooked, we never observe it to be angular as in lightning. The reason of this is, that there is no proportion between the capacity of the air for yielding to the impetus of lightning, and the velocity with which the latter is moved. From Mr Robins's experiments in gunnery, it appears, that the air cannot yield with a velocity much greater than 1200 feet in a second, and that all projectiles moving with a greater degree of velocity meet with a violent resistance. But if we suppose lightning to move only with one half the velocity of light, that is, near 100,000 miles in a second, or even with that of 1000 miles in a minute, which most probably is the case*, its motion in the fluid atmosphere will meet with a resistance very little inferior to what air would meet with in passing through the most solid bodies. The smallest difference of the resistance of the atmosphere on either side, must determine the lightning to that side; and in its passage to that new place where the resistance is least, it must pass on in a straight line, making an angle with its former course, because the atmosphere is altogether incapable of yielding with such rapidity as the electric matter requires, and therefore resists like a solid rock. The case is otherwise in the former examples: for tho' a small difference in the resistance forces the bubbles of air or steam to deviate from side to side, yet there is always a considerable proportion between the capacity of water for yielding, and that force by which the bubbles urge it to yield; so that though it does make a resistance sufficient to prevent the bubbles from moving in a straight line, yet it also perceptibly yields at all times, and therefore the tract of the bubbles is formed by a number of curves and not angles.

Hence we may understand the reason why the zig-zag kind of lightning is so dangerous, namely, because it must overcome a very violent resistance of the atmosphere; and wherever that resistance is in the very dangerous degree lessened, there it will undoubtedly strike, and at a very considerable distance too. It is otherwise with that kind which appears in flashes of no determinate form. The electric matter of which these are composed, is evidently dissipated in the air by some conducting substances which are present there; and of consequence, though a man, or other conducting body, happened to be very near such a flash, he would not be struck or materially injured by it, though a zig-zag flash, in such circumstances, would have probably discharged its whole force upon him.

The most destructive kind of lightning, however, as we have already observed, is that which assumes the form of balls. These are produced by an exceeding form of great power of electricity gradually accumulated till balls. The resistance of the atmosphere is no longer able to confine it. In general, the lightning breaks out from the electrified cloud by means of the approach of some conducting substance; either a cloud, or some terrestrial substance: but the fire-balls seem to be formed, not because there is any substance at hand to attract the electric matter from the cloud, but because the electricity is accumulated in such quantity that the cloud itself can no longer contain it. Hence such balls fly off slowly, and have no particular destination. Their appearance indicates a prodigious commotion and accumulation of electricity in the atmosphere, without a proportionable disposition in the earth to receive it. This disposition, however, we know, is perpetually altered by a thousand circumstances, and the place which first becomes most capable of admitting electricity will certainly receive a fire-ball. Hence this kind of lightning has been known to move slowly backwards and forwards in the air for a considerable space of time, and then suddenly to fall on one or more houses, according to their being more or less affected with an electricity opposite to that of the ball at the time. It will also run along the ground, break into several parts, and produce several explosions at the same time.

It is very difficult to imitate lightning of this kind in our electrical experiments. The only cases in which it hath been done in any degree are those in which Dr Priestley made the explosion of a battery pass for a considerable way over the surface of raw flesh, water, &c. and in Mr Arden's experiments, when a fire-ball ascended to the top of an electrified jar, and burst it; with a violent explosion. See Electricity n° 89, &c. In these cases, if, while the electric flash passed over the surface of the flesh, it had been possible to interrupt the metallic circuit by taking away the chain, the electric matter discharged from the battery would have been precisely in the situation of one of the fire-balls. Lightning balls above-mentioned; i.e., it would have been at a loss for a conductor. The negative side of the battery was the place of its destination; but to that it would not have easily got, because of the great quantity of atmosphere which lay in its way, and the incapacity of the neighbouring bodies to receive it. But, while the electric matter was thus stationary for want of a conductor, if any person standing near, or touching the negative side of the battery, presented a finger to that seemingly inoffensive luminous body, he would instantly be struck very violently; because a free communication being now made by means of his body, the powers by which the electric fluid is impelled from one place to another would instantly urge it upon him. But if we suppose a person, who hath no communication with the battery, to present his finger to the same body, he may perhaps receive a slight spark from it; but not a shock of any consequence, because there is not a perfect communication by means of his body with the place to which the electric fire is destined.

Hence we may account for the seemingly capricious nature of lightning of all kinds, but especially of that kind which appears in the form of balls. Sometimes it will strike trees, high houses, steeples, and towers, without touching cottages, men, or other animals, who are in the neighbourhood. In such cases, people would be apt to say that the neighbourhood of these higher objects prevented the others from the stroke; but with little reason, since low houses, men walking in the fields, cattle, nay the surface of the earth itself, have all been struck, while high trees and steeples in the neighbourhood have not been touched. In like manner, fire-balls have passed very near certain persons without hurting them, while they have, as it were, gone considerably out of their way to kill others. The reason of all this is, that in thunder-storms there is constantly a certain zone of earth considerably under the surface, which the lightning desires (if we may use the expression) to strike, because it hath an electricity opposite to that of the lightning itself. Those objects, therefore, which form the most perfect conductors between the electrified clouds and that zone of earth, will be struck by the lightning, whether they are high or low; and because we know not the conducting quality of the different terrestrial substances, the superstitious are apt to ascribe strokes of lightning to the divine vengeance against particular persons, whereas it is certain that this fluid, as well as others, acts according to invariable rules from which it is never known to depart.

the time of severe thunder-storms, is supposed to proceed from the earth, as well as from the clouds; but this fact hath never been well ascertained, and indeed from the nature of the thing it seems very difficult to be ascertained; for the motion of the electric fluid is so very quick, that it is altogether impossible to determine, by means of our senses, whether it goes from the earth or comes to it. In fact, there are in this country many thunder-storms in which it doth not appear that the lightning touches any part of the earth, and consequently can neither go to it nor come out from it. In these cases, it flashes either from an electrified cloud to one endowed with an opposite electricity, or merely into those parts of the atmosphere which are ready to receive it. But if not only the clouds, but the atmosphere all the way betwixt them and the earth, and likewise for a considerable space above the clouds, are electrified one way, the earth must then be struck. The reason of this will appear from a consideration of the principles laid down under the article Electricity, sect. vi. It there appears, that the electric fluid is altogether incapable either of accumulation or diminution in quantity in any particular part of space. What we call electricity is only the motion of this fluid made perceptible to our senses. Positive electricity is when the current of electric matter is directed from the electrified body. Negative electricity is when the current is directed towards it.

Let us now suppose, that a positively electrified cloud is formed over a certain part of the earth's surface. The electric matter flows out from it first into the atmosphere all round; and while it is doing so, the atmosphere is negatively electrified. In proportion, however, as the electric current pervades greater and greater portions of the atmospheric space, the greater is the resistance to its motion, till at last the air becomes positively electrified as well as the cloud, and then both act together as one body. The surface of the earth then begins to be affected, and it silently receives the electric matter by means of the trees, grass, &c. till at last it becomes positively electrified also, and begins to send off a current of electricity from the surface downwards. The causes which at first produced the electricity of the clouds (and which are treated of under the article Thunder), still continuing to act, the power of the electric current becomes inconceivably great. The danger of the thunder-storm now begins; for as the force of the lightning is directed to some place below the surface of the earth, it will certainly dart towards that place, and shatter every thing to pieces which retards its passage. The benefit of conducting-rods will now also be evident; for we are sure that the electric matter will in all cases take the way where it meets with the least resistance; and this is through the substance, or rather over the surface, of metals. In such a case, therefore, if there happen to be a house furnished with a conductor directly below the cloud, and at the same time a zone of negatively electrified earth not very far below the foundation of the house, the conductor will almost certainly be struck, but the building will be unhurt. If the house wants a conductor, the lightning will nevertheless strike in the same place, in order to get at the negatively electrified zone above mentioned; but the building will now be damaged, because the materials of it cannot readily conduct the electric fluid.

We will now be able to enter into the dispute, Whether the preference is due to knopped or pointed conductors for preserving buildings from strokes of lightning? Ever since the discovery of the identity of electricity and lightning, it hath been allowed by all respectable parties, that conductors of some kind are in a manner essentially necessary for the safety of buildings in those countries where thunder-storms are very frequent. The principle on which they act hath been already explained; namely, that the electric fluid, when impelled by any power, always goes to that place where Lightning it meets with the least resistance, as all other fluids also do. As metals, therefore, are found to give the least resistance to its passage, it will always choose to run along a metallic rod, in preference to a passage of any other kind. We must, however, carefully consider a circumstance which seems to have been too much overlooked by electricians in their reasonings concerning the effects of thunder-rods; namely, that lightning, or electricity, never strikes a body, merely for the sake of the body itself, but only because by means of that body it can readily arrive at the place of its destination. When a quantity of electricity is collected from the earth, by means of an electric machine, a body communicating with the earth will receive a strong spark from the prime conductor. The body receives this spark, not because it is itself capable of containing all the electricity of the conductor and cylinder, but because the natural situation of the fluid being disturbed by the motion of the machine, a stream of it is sent off from the earth. The natural powers, therefore, make an effort to supply what is thus drained off from the earth; and as the individual quantity which comes out is most proper for supplying the deficiency, as not being employed in any natural purpose, there is always an effort made for returning it to the earth. No sooner, then, is a conducting body, communicating with the earth, presented to the electrical machine, than the whole effort of the electricity is directed against that body, not merely because it is a conductor, but because it leads to the place where the fluid is directed by the natural powers by which it is governed, and at which it would find other means to arrive, though that body were not to be presented. That this is the case, we may very easily satisfy ourselves, by presenting the very same conducting substance in an inflated state to the prime conductor of the machine; for then we shall find, that only a very small spark will be produced.

In like manner, when lightning strikes a tree, a house, or a thunder-rod, it is not because these objects are high, or in the neighbourhood of the cloud; but because they communicate with some place below the surface of the ground, against which the impetus of the lightning is directed; and at that place the lightning would certainly arrive, though none of the above-mentioned objects had been interposed.

The fallacy of that kind of reasoning generally employed concerning the use of thunder-rods, will now be sufficiently apparent. Because a point presented to an electrified body in our experiments, always draws off the electricity in a silent manner; therefore Dr Franklin and his followers have concluded, that a pointed conductor will do the same thing to a thunder-cloud, and thus effectually prevent any kind of danger from a stroke of lightning. Their reasoning on this subject, they think, is confirmed by the following fact among many others. "Dr Franklin's house at Philadelphia was furnished with a rod extending nine feet above the top of the chimney. To this rod was connected a wire of the thickness of a goose-quill, which descended through the wall of the stair-case; where an interruption was made, so that the ends of the wire, to each of which a little bell was fixed, were distant from each other about six inches; an insulated brass ball hanging between the two bells. The author was one night waked by loud cracks, proceeding from his apparatus in the stair-case. He perceived, that the brass ball, instead of vibrating as usual between the bells, was repelled and kept at a distance from both; while the fire sometimes passed in very large quick cracks directly from bell to bell; and sometimes in a continued dense white stream, seemingly as large as his finger; by means of which the whole stair-case was enlightened, as with sun-shine, so that he could see to pick up a pin.—From the apparent quantity of electric matter of which the cloud was thus evidently robbed, by means of the pointed rod (and of which a blunt conductor would not have deprived it), the author conceives, that a number of such conductors must considerably lessen the quantity of electric fluid contained in any approaching cloud, before it comes to near as to deliver its contents in a general stroke."

For this very reason, Mr Benjamin Wilson and his followers, who constitute the opposite party, have determined that the use of pointed conductors is utterly unsafe. They say, that in violent thunder storms the whole atmosphere is full of electricity; and that attempts to exhaust the vast quantity there collected, are like attempting to clear away an inundation with a shovel, or to exhaust the atmosphere with a pair of bellows. They maintain, that though pointed bodies will effectually prevent the accumulation of electricity in any substance; yet if a non-electrified body is interposed between a point and the conductor of an electrical machine, the point will be struck at the same moment with the non-electrified body, and at a much greater distance than that at which a knob would be struck. They affirm also, that, by means of this silent solicitation of the lightning, inflammable bodies, such as gun-powder, tinder, and Kunckel's phosphorus, may be set on fire; and for these last facts they bring decisive experiments. From all this, say they, it is evident that the use of pointed conductors is unsafe. They solicit a discharge to the place where they are; and as they are unable to conduct the whole electricity in the atmosphere, it is impossible for us to know whether the discharge they solicit may not be too great for our conductor to bear; and consequently all the mischiefs arising from thunder-storms may be expected, with this additional and mortifying circumstance, that this very conductor hath probably solicited the fatal stroke, when without it the cloud might have passed harmlessly over our heads without striking at all.

Here the reasoning of both parties seems equally wrong. They both proceed on this erroneous principle, that in thunder-storms the conductor will always solicit a discharge, or that at such times all the elevated objects on the surface of the earth are drawing off the electricity of the atmosphere. But this cannot be the case, unless the electricity of the earth and of the atmosphere is of a different kind. Now, it is demonstrable, that until this difference between the electricity of the atmosphere and of the surface of the earth ceases, there cannot be a thunder-storm. When the atmosphere begins to be electrified either positively or negatively, the earth, by means of the inequalities and moisture of its surface, but especially by the vegetables which grow Lightning grow upon it, absorbs that electricity, and quickly becomes electrified in the same manner with the atmosphere. This absorption, however, ceases in a very short time, because it cannot be continued without setting in motion the whole of the electric matter contained in the earth itself. Alternate zones of positive and negative electricity will then begin to take place below the surface of the earth, for the reasons mentioned under the article Electricity, sect. vi. § 9. Between the atmosphere and one of these zones, the stroke of the lightning always will be. Thus supposing the atmosphere is positively electrified, the surface of the earth will, by means of trees, &c., quickly become positively electrified also; we shall suppose to the depth of 10 feet. The electricity cannot penetrate farther on account of the resistance of the electric matter in the bowels of the earth.

At the depth of 10 feet from the surface, therefore, a zone of negatively electrified earth begins, and to this zone the electricity of the atmosphere is attracted; but to this it cannot get, without breaking through the positively electrified zone which lies uppermost, and shattering to pieces every bad conductor which comes in its way. We are very sure, therefore, that in whatever places the outer-zone of positively electrified earth is thinner, there the lightning will strike, whether a conductor happens to be present or not. If there is a conductor, either knobbed or sharp-pointed, the lightning will indeed infallibly strike it; but it would also have struck a house situated on that spot, without any conductor; and though the house had not been there, it would have struck the surface of the ground itself.—Again, if we suppose the house with its conductor to stand on a part of the ground where the positively electrified zone is very thick, the conductor will neither silently draw off the electricity, nor will the lightning strike it, though perhaps it may strike a much lower object, or even the surface of the ground itself, at no great distance; the reason of which undoubtedly is, that there the zone of positively electrified earth is thinner than where the conductor was.

We must also observe, that the Franklinians make their pointed conductors to be of too great consequence. To the houses on which they are fixed, no doubt, their importance is very great; but in exhausting a thunder-cloud of its electricity, their use must appear trifling; and to insist on it, ridiculous. Innumerable objects, as trees, grass, &c., are all conspiring to draw off the electricity, as well as the conductor, if it could be drawn off; but of effecting this there is an impossibility, because they have the same kind of electricity with the clouds themselves. The conductor hath not even the power of attracting the lightning a few feet out of the direction which it would choose of itself. Of this we have a most remarkable and decisive instance in what happened to the magazine at Purfleet in Essex, on May 15, 1777. That house was furnished with a pointed conductor, raised above the highest part of the building; nevertheless, about six in the evening of the abovementioned day, a flash of lightning struck an iron cramp in the corner of the wall considerably lower than the top of the conductor, and only 46 feet in a sloping line distant from the point.—This produced a long dispute with Mr Wilton concerning the propriety of using pointed conductors; and, by the favour of his majesty, he was enabled to construct a more magnificent electrical apparatus than any private person could be supposed to erect at his own expense, and of which some account is given under the article Electricity, no 83. The only new experiments, however, which this apparatus produced, were the firing of gunpowder by the electric aura, as it is called; and a particularly violent shock which a person received when he held a small pointed wire in his hand, upon which the conductor was discharged. We must observe, that the electrified surface of the conductor was 620 feet; and we can have but little idea of the strength of sparks from a conductor of this magnitude, supposing it properly electrified. Six turns of the wheel made the discharge felt through the whole body like the strong shock of a Leyden vial; and nobody chose to make the experiment when the conductor had received a higher charge. A very strong shock was felt, as already observed, when this conductor was discharged upon a pointed wire held in a person's hand, even though the wire communicated with the earth; which was not felt, or but very little, when a knotted wire was made use of. To account for this difference may, perhaps, puzzle electricians; but with regard to the use of blunt or pointed thunder-rods, both experiments seem quite inconclusive. Though a very great quantity of electric matter silently drawn off will fire gunpowder, this only proves that a pointed conductor ought not to pass through a barrel of gunpowder; and if a person holding a pointed wire in his hand received a strong shock from Mr Wilton's great conductor, it can thence only be inferred, that in the time of thunder nobody ought to hold the conductor in their hands; both which precautions common sense would dictate without any experiment. From the accident at Purfleet, however, the disputants on both sides ought to have seen, that, with regard to lightning, neither points nor knobs can attract. Mr Wilton surely had no reason to condemn the pointed conductor for soliciting the flash of lightning, seeing it did not strike the point of the conductor, but a blunt cramp of iron; neither have the Franklinians any reason to boast of its effect in silently drawing off the electric matter, since all its powers were neither able to prevent the flash, nor to turn it 46 feet out of its way. The matter of fact is, the lightning was determined to enter the earth at the place where the board-house stands, or near it. The conductor fixed on the house offered the easiest communication; but 46 feet of air intervening between the point of the conductor and the place of explosion, the resistance was less through the blunt cramp of iron, and a few bricks moistened with rainwater, to the side of the metallic conductor, than through the 46 feet of air to its point; for the former was the way in which the lightning actually passed.

Mr Wilton and his followers seem also mistaken in supposing that a pointed conductor can solicit a greater discharge than what would otherwise happen. Allowing the quantity of electricity in the atmosphere during the time of a thunder-storm to be as great as they please to suppose; nevertheless, it is impossible that the air can part with all its electricity at once, on account of the difficulty with which the fluid moves in it. A pointed conductor, therefore, if it does anything at all, can only solicit the partial discharge which which is to be made at any rate; and if none were to be made though the conductor was absent, its presence will not be able to effect any.

An objection to the use of conductors, whether blunt or pointed, may be drawn from the accident which happened to the poor-house at Heckingham, which was struck by lightning through furnished with eight pointed conductors; but from an accurate consideration of the manner in which the conductors were situated, it appears, that there was not a possibility of their preventing any stroke. See Philosophical Transactions, Vol. LXXII. p. 361.

In a late publication on the subject of electricity by Lord Mahon, we find a new kind of lightning made mention of, which he is of opinion may give a fatal stroke, even though the main explosion be at a considerable distance; a mile, for instance, or more. This he calls the electrical returning stroke; and exemplifies it in the following manner, from some experiments made with a very powerful electrical machine, the prime conductor of which (six feet long, by one foot diameter) would generally, when the weather was favourable, strike into a brass ball connected with the earth, to the distance of 18 inches or more. In the following account, this brass ball, which we shall call A, is supposed to be constantly placed at the striking distance; so that the prime conductor, the instant that it becomes fully charged, explodes into it.

Another large conductor, which we shall call the second conductor, is suspended, in a perfectly insulated state, farther from the prime conductor than the striking distance, but within its electrical atmosphere; at the distance of six feet, for instance. A person standing on an insulating stool touches this second conductor very lightly with a finger of his right hand; while, with a finger of his left hand, he communicates with the earth, by touching very lightly a second brass ball fixed at the top of a metallic stand, on the floor, and which we shall call B.

While the prime conductor is receiving its electricity, sparks pass (at least if the distance between the two conductors is not too great) from the second conductor to the insulated person's right hand; while similar and simultaneous sparks pass out from the finger of his left hand into the second metallic ball B, communicating with the earth. These sparks are part of the natural quantity of electric matter belonging to the second conductor, and to the insulated person; driven from them into the earth, through the ball B, and its stand, by the elastic pressure or action of the electrical atmosphere of the prime conductor. The second conductor and the insulated person are hereby reduced to a negative state.

At length, however, the prime conductor, having acquired its full charge, suddenly strikes into the ball A, of the first metallic stand, placed for that purpose at the striking distance of 17 or 18 inches. The explosion being made, and the prime conductor suddenly robbed of its electric atmosphere, its pressure or action on the second conductor, and on the insulated person, as suddenly ceases; and the latter instantly feels a smart returning stroke, though he has no direct or visible communication (except by the floor) either with the striking or struck body, and is placed at the distance of five or six feet from both of them. This returning stroke is evidently occasioned by the sudden re-entrance of the Lightning-electric fire naturally belonging to his body and to the second conductor, which had before been expelled from them by the action of the charged prime conductor upon them; and which returns to its former place the instant that action or elastic pressure ceases. The author shows, that there can be no reason to suppose that the electrical discharge from the prime conductor should in this experiment divide itself at the instant of the explosion, and go different ways, so as to strike the second conductor and insulated person in this manner, and at such a distance from it.

When the second conductor and the insulated person are placed in the densest part of the electrical atmosphere of the prime conductor, or just beyond the striking distance, the effects are still more considerable; the returning stroke being extremely severe and pungent, and appearing considerably sharper than even the main stroke itself, received directly from the prime conductor. This circumstance the author alleges as an unanswerable proof that the effect which he calls the returning stroke, was not produced by the main stroke being any wise divided at the time of the explosion, since no effect can ever be greater than the cause by which it is immediately produced.—Having taken the returning stroke eight or ten times one morning, he felt a considerable degree of pain across his chest during the whole evening, and a disagreeable sensation in his arms and wrists all the next day.

We come now to the application of this experiment, and of the doctrine deduced from it, to what passes in natural electricity, or during a thunder-storm; in which there is reason to expect similar effects, but on a larger scale—a scale so large indeed, according to the author's representation, that persons and animals may be destroyed, and particular parts of buildings may be considerably damaged, by an electrical returning stroke, occasioned even by some very distant explosion from a thunder-cloud:—possibly at the distance of a mile or more.

It is certainly easy to conceive, that a charged extensive thunder-cloud must be productive of effects similar to those produced by the author's prime conductor. Like it, while it continues charged, it will, by the superinduced elastic electrical pressure of its atmosphere, to use the author's own expression, drive into the earth a part of the electric fluid naturally belonging to the bodies which are within the reach of its widely extended atmosphere; and which will therefore become negatively electrical. This portion too of their electric fire, as in the artificial experiments, will, on the explosion of the cloud, at a distance, and the cessation of its action upon them, suddenly return to them; so as to produce an equilibrium, and restore them to their natural state.

To this theory, the authors of the Monthly Review answered have given the following answer: "We cannot, however, agree with the ingenious author, with respect to viewers, the greatness of the effects, or of the danger to be apprehended from the returning stroke in this case; as we think his estimate is grounded on an erroneous foundation.—Since (says he) the density of the electrical atmosphere of a thunder-cloud is so immense, when compared to the electrical density of the electrical atmosphere of any prime conductor, charged by means of any elec- In the case of a man who is abroad, and in an open field, during the time of an explosion—as he is unconnected with other masses of matter above him, no more than the precise quantity of electric fire, which had been before expelled from his body, will suddenly return into it at the instant of a distant explosion: and that this quantity is not usually very large, may be inferred from many considerations.

When a person standing on the ground holds a pair of Mr Canton's balls in his hand, while a highly charged thunder-cloud is suspended over his head; the angle made by the balls indicates the electrical state of that person, or the quantity of natural electricity of which his body is at that time deprived, by the action of the (positively) charged cloud hanging over him. But we have never seen the repulsion of the balls so considerable, as to furnish any just apprehensions that the return of his natural electric matter, however sudden, could be attended with injury to him: nor would he be sensible of any commotion on the balls suddenly coming together; though a spark might undoubtedly be perceived, at that instant, were he inflamed, and placed in the same manner with the author when he tried the above-related experiment.

The author nevertheless observes, that there have been instances of persons who have been killed by natural electricity, having been found with their feet torn, and with their feet damaged by the electrical fire; but who have not had, over their whole body, any other apparent marks of having been struck with lightning. He adds, if a man walking out of doors were to be killed by a returning stroke, the electrical fire would rush into that man's body through his feet, and his feet only; which would not be the case, were he to be killed by any main stroke of explosion, either positive or negative.

It would be no difficult task, we think, to account for these appearances in a different manner; were all the circumstances attending the case minutely ascertained: but without interrogating the dead on this subject, we may more satisfactorily appeal to the experience of the living (p), to show, that though the returning stroke must take place, in all thunder-storms, in some degree or other; yet it is not of that alarming magnitude which the author ascribes to it. If, in any particular thunder-storm, a man in the open fields could be killed, at the instant of a distant explosion, merely by the return of his own electric fire, which had before been driven out of his body; surely numerous observations of persons who had experienced the returning stroke, in lighter degrees, would be familiar; and scarce a great thunder-storm must have occurred, in which

(c) "We suppose the person not to be so situated, that the returning fire of other bodies must necessarily pass through his body."

(d) "The author does indeed produce a living evidence, in the case of a person at Vienna, who, he has been credibly informed, received an electrical shock, by having held one hand accidentally in contact with an interrupted metallic conducting rod, at the instant that a thunder-cloud exploded at the distance, as was conjectured, of above half an English mile. He likewise observes, that a 'very strong, bright, and sudden stroke' (or spark) of electrical fire has been seen, by several electricians, to pass in the interval, or interruption, purposely left in the conducting rod of a house at the instant of a distant explosion; and 'when it was fully proved, by the sharp point of the conductor not being melted, or even tinged,' that the conductor itself had not been struck.—These observations, however, do not by any means prove the magnitude or danger of the returning stroke, but merely its existence; which we do not contest." Lightning: one person or another must not, at the instant of an explosion, have felt the effects of the returning stroke, in some degree or other—from that of a violent concussion, to that of a slight and almost imperceptible pulsation. But no observations of this kind are known to us; nor have we ever heard of any person's experiencing any kind of electrical commotion in a thunder-storm, except such as have either been directly struck, or have happened to be in the very near neighbourhood of the spot where the explosion took place.

"The author has been aware of this objection, which he proposes, and endeavours to remove: but his answer to it amounts to little more than what has been already quoted from him; that is, to a simple estimate of the enormous difference between the electrical density, or the elastic electrical pressure, of the atmosphere of an extensive thunder cloud, and that of a charged prime conductor. We have already observed, that this is not the proper method of estimating their different effects, when these two causes, how unequal soever in power, are considered as exerting that power on bodies containing a limited and comparatively small quantity of electric matter.

"We have been induced to discuss this subject thus particularly, with a view to quiet the minds of the timorous; as the author's extension of his principles, respecting the returning stroke in artificial electricity, to what passes in natural electricity, holds out a new, and, in our opinion, groundless subject of terror to those who, in the midst of their apprehensions, have hitherto only dreaded the effects of a thunder-storm when it made near approaches to them; but who, if this doctrine were believed, would never think themselves in security while a thunder-cloud appeared in sight, unless sheltered in a house furnished with proper conductors:—for we should not omit to remark, that a subsequent observation tends to diminish their fears, by showing that high and pointed conductors tend to secure both persons and buildings against the various effects of any returning stroke whatever, as well as of the main stroke."

A late melancholy accident which happened in Scotland has afforded Lord Mahon an opportunity of bringing additional arguments in favour of his system. An account of this accident is given by Patrick Brydone, Esq.; R. S. in the 77th volume of the Philosophical Transactions. It happened on the 19th of July 1785, near Coldstream on the Tweed. The morning was fine, with the thermometer at 68°; but about eleven o'clock the sky became obscured with clouds in the south-east: and betwixt twelve and one a storm of thunder and lightning came on. This storm was at a considerable distance from Mr Brydone's house, the intervals between the flash and crack being from 25 to 30 seconds, so that the place of explosion must have been betwixt five and six miles off: but while our author was observing the progress of the storm, he was suddenly surprised with a loud report, neither preceded nor accompanied by any flash of lightning, which resembled the explosion of a great number of muskets, in such quick succession, that the ear could scarcely discriminate the sounds. On this the thunder and lightning instantly ceased, the clouds began to separate, and the sky soon recovered its serenity. In a little time Mr Brydone was informed, that a man with two horses had been killed by the thunder; and, on running out to the place, our author found the two horses lying on the spot where they had been first struck, and still yoked to the cart. As the body of the man who was killed had been carried off, Mr Brydone himself had not an opportunity of examining it, but was informed by Mr Bell, minister of Coldstream, who saw it, that the skin of the right thigh was much burnt and shrivelled; that there were many marks of the same kind all over the body, but none on the legs: his clothes, particularly his shirt, had a strong smell of burning; and there was a zig-zag line of about an inch and a quarter broad, extending from the chin to the right thigh, and which seemed to have followed the direction of the buttons of his waistcoat. The body was buried in two days without any appearance of putrefaction.

Mr Brydone was informed by another person who accompanied him that was killed, of the particular circumstances. They were both driving carts loaded with coals; and James Lauder, the person who was killed, had the charge of the foremost cart, and was fitting on the fore part of it. They had crossed the Tweed a few minutes before at a deep ford, and had almost gained the highest part of an ascent of about 65 or 70 feet above the bed of the river, when he was stunned with the report above mentioned, and saw his companion with the horses and cart fall down. On running up to him, he found him quite dead, with his face livid, his clothes torn in pieces, and a great smell of burning about him. At the time of the explosion he was but about 24 yards distant from Lauder's cart, and had him full in view when he fell, but felt no shock, neither did he perceive any flash or appearance of fire. At the time of the explosion his horses turned round, and broke their harness. The horses had fallen on their left side, and their legs had made a deep impression on the dust; which, on lifting them up, showed the exact form of each leg, so that every principle of life seemed to have been extinguished at once, without the least struggle or convulsive motion. The hair was singed over the greatest part of their bodies, but was most perceptible on their belly and legs. Their eyes were dull and opaque, as if they had been long dead, though Mr Brydone saw them in half an hour after the accident happened. The joints were all supple, and he could not observe that any of the bones were broken or dislocated, as is said to be sometimes the case with those who are killed by lightning. The left shaft of the cart was broken, and splinters had been thrown off in many places; particularly where the timber of the cart was connected by nails or cramps of iron. Many pieces of the coal were thrown to a considerable distance; and some of them had the appearance of being some time on a fire. Lauder's hat was torn into innumerable small pieces; and some part of his hair was strongly united to those which had composed the crown of it. About four feet and a half behind each wheel of the cart he observed a circular hole of about 20 inches diameter, the centre of which was exactly in the track of each wheel. The earth was torn up as if by violent blows of a pick-axe; and the small stones and dust were scattered on each side of the road. The tracks of the wheels were strongly marked in the dust, both before and behind these holes, but did not in the smallest Lightning smallest degree appear on the spots themselves for upwards of a foot and a half. There were evident marks of fusion on the iron rings of the wheels; the surface of the iron, the whole breadth of the wheel, and for the length of about three inches, was become bluish, had lost its polish and smoothness, and was formed into drops which projected sensibly, and had a roundish form; but the wood did not appear any way injured by the heat which the iron must have conceived. To determine whether these were made by the explosion which had torn up the ground, the cart was pushed back on the same track which it had described on the road; and the marks of fusion were found exactly to correspond with the centres of the holes. They had made almost half a revolution after the explosion; which our author attributes to the cart being pulled a little forward by the fall of the horses. Nothing remarkable was observed on the opposite part of the wheel. The broken ground had a smell something like that of ether; the soil itself was very dry and gravelly.

The catastrophe was likewise observed by a shepherd, at the distance of about 200 or 300 yards from the spot. He said, that he was looking at the two carts going up the bank when he heard the report, and saw the foremost man and horses fall down; but observed no lightning, nor the least appearance of fire, only he saw the dust rise about the place. There had been several flashes of lightning before that from the south-east; whereas the accident happened to the north-west of the place where he stood. He was not sensible of any shock.

Our author next gives an account of several phenomena which happened the same day, and which were evidently connected with the explosion. A shepherd tending his flock in the neighbourhood, observed a lamb drop down; and said, that he felt at the same time as if fire had passed over his face, though the lightning and claps of thunder were at a considerable distance. He ran up to the creature immediately, but found it quite dead; on which he bled it with his knife, and the blood flowed freely. The cart was not torn up; nor did he observe any dust rise, though he was only a few yards distant. This happened about a quarter of an hour before Lauder was killed, and the place was only about 300 yards distant.

About an hour before the explosion, two men standing in the middle of the Tweed, fishing for salmon, were caught in a violent whirlwind, which felt sultry and hot, and almost prevented them from breathing. They could not reach the bank without much difficulty and fatigue; but the whirlwind lasted only a very short time, and was succeeded by a perfect calm.

A woman making hay, near the banks of the river, fell suddenly to the ground, and called out that she had received a violent blow on the foot, and could not imagine from whence it came; and Mr Bell, the minister above mentioned, when walking in his garden, a little before the accident happened to Lauder, felt several times a tremor in the ground.

The conclusion drawn from these facts by Brydone is, that at the time of the explosion the equilibrium between the earth and the atmosphere seems to have been completely restored, as no more thunder was heard nor lightning observed; the clouds were dispersed, and the atmosphere resumed the most perfect tranquillity: "But how this vast quantity of electric matter (says he) could be discharged from the one ele-

Lord Malton, now Earl Stanhope, whose observations on this accident are published in the same volume, endeavours to establish the following positions as facts:

1. That the man and horses were not killed by any direct main stroke of explosion from a thunder-cloud either positively or negatively electrified.

2. They were not killed by any transmitted main stroke either positive or negative.

3. The mischief was not done by any lateral explosion.

All these are evidently true, at least with respect to lightning at that time falling from the clouds; for all the lightning which had taken place before was at a great distance.

4. They were not suffocated by a sulphureous vapour or smell which frequently accompanies electricity. This could not account for the pieces of coal being thrown to a considerable distance all round the cart, and for the splinters of the wood which were thrown off from many parts of the cart.

5. It might be imagined by some that they were killed by the violent commotion of the atmosphere, occasioned by the vicinity of the electrical explosion, in a manner similar to the fatal wounds that sometimes have been known to have been given by the air having been suddenly displaced by a cannon-ball in its passage through the atmospherical fluid, though the cannon-ball itself had evidently neither struck the person wounded nor grazed his clothes. The dust that rose at the time of the explosion might be brought as an argument in favour of the opinion, that a sudden and violent commotion of the air did occasion the effects produced. But such an explanation would not account for the marks of fusion on the iron of the wheels, nor for the hair of the horses being singed, nor for the skin of Lauder's body having been burnt in several places.

6. From these different circumstances his lordship is of opinion, that the effects proceeded from electricity; and that no electrical fire did pass immediately, either from the clouds into the cart, or from the cart into the clouds. From the circular holes in the ground, of about 20 inches diameter, the respective centres of which were exactly in the track of each wheel, and the corresponding marks of fusion in the iron of the wheels, it is evident that the electrical fire did pass from the earth to the cart, or from the cart to the earth, through that part of the iron of the wheels which was in contact with the ground. From the splinters which had been thrown off in many places, particularly where the timber was connected by nails or cramps of iron, and from various other effects mentioned in Mr Brydone's account, it is evident, that there must have been a great commotion in the electrical fluid in all, or at least in different parts of the cart, and in the bodies of the man and horses, although there were no lightning.

7. All these phenomena, his lordship argues, may be explained in a satisfactory manner from the doctrine already Lightning, already laid down concerning the returning stroke. Before entering upon the subject of the main explosion, however, he takes notice of the other phenomena already mentioned in Mr Brydone's account.

With regard to the case of the lamb, his lordship is of opinion, that it belongs to the most simple class of returning strokes, viz. that which happens at a place where there is neither thunder nor lightning near; and that it may be produced by the sudden removal of the elastic electrical pressure of the electrical atmosphere of a single main cloud, as well as of an assemblage of clouds. It appears (says he) by Mr Brydone's account, that the shepherd who saw the lamb fall, was near enough to it to feel, in a small degree, the electrical returning stroke at the same time that the lamb dropped down.

The blow which the woman received on the foot was unquestionably the returning stroke. When a person walking, or standing, out of doors, is knocked down or killed by the returning stroke, the electrical fire must rush in, or rush out, as the case may be, through that person's feet, and through them only; which would not be the case were the person to be killed by any main stroke of explosion either positive or negative.

8. In order to account for the manner in which the man and horses were killed, his lordship premised, that, according to Mr Brydone's account, the cloud must have been many miles in length; insomuch as just before the report, the lightning was at a considerable distance, viz. between five and six miles. The loud report resembled the firing of several muskets so close together, that the ear could scarcely separate the sounds, and was followed by no rumbling noise like the other claps. This indicates, that the explosion was not far distant, and likewise that it was not extremely near; for, if the explosion had been very near, the ear could not at all have separated the sounds.

9. Let us now suppose a cloud, eight, ten, or twelve miles in length to be extended over the earth, and let another cloud be situated betwixt that and the earth; let them also be supposed charged with the same kind of electricity, and both positive. Let us farther suppose the lower cloud to be near the earth, only a little beyond the striking distance; and the man, cart, and horses, to be situated under that part of the cloud which is next the earth, and to be exactly as described by Mr Brydone, viz. near the summit of a hill, and followed by another a little farther down; and let us suppose the two clouds to be near each other just over the place where the man and horses are: Let the remote end of the cloud approach the earth, and discharge its electricity into it. In this case the following effects will take place.

10. When the upper cloud discharges its electricity into the earth from the remote end, the lower cloud will discharge its electricity into the nearer end of the upper cloud, which is supposed to be directly over the place of the cart and horses, or nearly so. This accounts for the loud report of thunder that was unaccompanied by lightning. The report must be loud from its being near; but no lightning could be perceived, by reason of the thick cloud situated immediately between the spectator and the space betwixt the two clouds where the lightning appears.

11. As the lower cloud gradually approached towards the earth, that part of the latter where the man and horses were, must of course become superinduced lightning, by the elastic electrical pressure of the electrical atmosphere of the thunder-cloud; which superinduced elastic electrical pressure must gradually have increased as the cloud came closer to the earth, and approached nearer to the limit of the striking distance.

12. Hence, if any conducting body (not having prominent or conducting points) were to be placed upon the surface of the earth, and there electrically insulated; then such conducting body, by the laws of electricity, must, at its upper extremity (namely the part nearest to the positive cloud) become negative; at its lower extremity it must become positive; and, at a certain intermediate point, it will be neither plus nor minus. This insulated conducting body, thus situated, will be in three opposite states at the same time, that is to say, it will be, at the same time, positively electrified, negatively electrified, and not electrified at all.—For a demonstration of this proposition, his lordship refers to his Principles of Electricity; but it is a generally known and established fact in electricity.

13. If this conducting body on the surface of the earth be not insulated, or be but imperfectly insulated, then the whole of such body, from its being immersed in the electrical atmosphere of the positive cloud, will become negative; because part of the electricity of the conducting body will in this case pass into the earth; and the conducting body will become the more negative as it becomes the more deeply immersed into the dense part of the elastic electrical atmosphere of the approaching thunder-cloud.

14. When the lower cloud comes suddenly to discharge with an explosion its superabundant electricity into the upper one, then the elastic electrical atmosphere of the former will cease to exist; consequently the electrical fluid, which had been gradually expelled into the common stock from the conducting body on the surface of the earth, must, by the sudden removal of the superinduced elastic electrical pressure of the electrical atmosphere of the thunder-cloud, suddenly return from the earth into the said conducting body, producing a violent commotion similar to the pungent shock of a Leyden jar in its sensation and effects.

15. This, which his lordship calls the electrical returning stroke, he supposes to have been what killed the effects of man and horses in the present case, they having become strongly negative before the explosion. The man, according to Mr Brydone's account, was sitting when he received the stroke, and his legs were hanging over the fore part of the cart at the time of the explosion. The returning stroke, therefore, could not enter his body through the legs; and this accounts for the skin of his legs not having been at all burnt or shrivelled, as the skin was on many other parts of his body; and it likewise shows the reason why the zig-zag line, which was terminated by the chin, did not extend lower than the thigh.

16. Mr Brydone likewise informs us, that the hair of the horses was much singed over the greatest part of their bodies, but was most perceptible on the belly and legs. This is easily accounted for by the returning stroke; for the lower part of the bodies of these animals must of course have been more affected than any other part, as the electrical fire must have rushed suddenly into their bodies through their legs, which had made a deep impression on the dust. 17. The various effects produced on the cart may be explained also from the returning stroke with equal facility. The splinters were thrown off by reason of the interruption of good conductors; the wood being a much less perfect conductor than the iron. It is also evident, that it was the electrical returning fire that produced the marks of fusion on that part of the iron of the wheels which was in contact with the ground; inasmuch as the whole electricity, at the instant of the explosion, did enter at these places.

18. No person in the least versed in the principles of electricity can hesitate to assent to the proposition, that the electrical returning stroke must exist under circumstances similar to those explained above; but it may be objected, as the reviewers formerly did, that the quantity of electricity naturally contained in the body of a man, &c. is by far too small to produce such violent effects. For an answer to this objection, his lordship refers to his book: By way of corroboration, however, he makes the following remarks.

19. No person can reasonably conclude, that the strength of force of a returning stroke must always be weak when produced by the disturbed electrical fluid of a man's body, by reason that a man's body contains but a small quantity of electricity: for it has never been proved that a man's body contains only a small quantity of electrical fluid; neither is there the smallest reason to believe such a hypothesis, which appears, on many accounts, to be completely erroneous; and if that hypothesis be erroneous, the objection to the strength of an electrical returning stroke remains altogether unsupported by argument. "When a body is said to be plus or positive (says his lordship), it simply means, that the body contains more than its natural share of electricity, but does not say that it is completely saturated with it. In like manner, when a body is said to be minus or negative, it only signifies, that the body contains less than its natural share of electricity; but does not imply that such body is completely exhausted of the electricity which it contains in its natural state. "Now (says he), the strength of natural electricity is so immense, when compared with the very weak effects of our largest and best contrived electrical machines, that I conceive we cannot, by means of artificial electricity, expel, from a man's body, thousandth, or perhaps the ten-thousandth part of the electrical fluid which it contains when in its natural state."

20. An hypothesis which easily accounts for any natural phenomenon has a much better claim to our attention than an opposite one, which prevents it from being intelligibly explained. There is no reason to conclude that any electrical machine, of any given size, is capable of rendering a conducting body either completely plus or completely minus; but far otherwise. And it would have been as logical for any person some years ago (when electrical machines were not brought to their present state) to have maintained, that those very imperfect machines were capable of rendering a body completely positive or completely negative, as for us to pretend to do it at this day. We evidently have not, with our machines, even approached the limit of electrical strength, particularly in respect to the returning stroke: for it is remarkable, that, by the laws of electricity, the strength of the electrical returning stroke, near the limit of the striking distance, does increase in a greater ratio than the strength of the main stroke from the charged body producing the elastic electrical atmosphere superinduced. Thus, let us attempt to produce the returning stroke by means of a metallic conductor of about the return stroke diameter; and by means of another metallic body of different dimensions placed parallel to the prime conductor, just out of the limit of the striking distance; and let the prime conductor be charged by one of the common glass globes of less than nine inches in diameter; the returning stroke in this case will be so weak, that it can hardly be said to exist: but if the experiment be made by means of a large cylinder, and by means of a metallic prime conductor of about three feet four inches long, by nearly four inches and an half diameter, and also by means of another metallic body of equal dimensions with this prime conductor, then there will be no kind of comparison betwixt the strength of the returning stroke obtained out of the striking distance, and the strength of the main stroke received immediately from the prime conductor; the sharpness and pungency of the returning stroke being so much superior. The returning stroke in this case is like the sudden discharge of a weakly electrified Leyden jar, provided due attention be paid to the rules for obtaining a strong returning stroke.

21. In the case of a returning stroke, the strength depends, according to his lordship's hypothesis, not so much on the quantity of the electric fluid, as on its velocity; whence also it depends less on the quantity of surface used than on the strength of the electrical pressure of the elastic electrical atmosphere superinduced upon the body struck previous to the explosion. But the electrical pressure of the elastic electrical atmosphere of the great thunder-cloud which produced the mischief on the present occasion, must have been immensely greater than that of a metallic prime conductor; and it is not surprising that the effects should be proportioned to the causes.

22. His lordship next accounts for the returning stroke not being felt by the man who followed Lauder's cart. This, he thinks, may in some degree be accounted for by the latter having been higher up the bank; though it may better be done by supposing the cloud to have been pending nearer the earth over the spot where Lauder was killed, than over the place where his companion was; for, in order to receive a dangerous returning stroke, it is necessary that he should be immersed, not merely in the cloud's atmosphere, but in the dense part of the cloud's electrical atmosphere. It may also be accounted for by supposing that the second cart were either better connected with the common stock, or better insulated; for either of these circumstances will weaken a returning stroke prodigiously. Now Mr Brydone mentions, that there had been an almost total want of rain for many months. He also says, that the ground, at the place where Lauder was killed, was remarkably dry, and of a gravelly soil. This state of the ground was particularly adapted to the production of the electrical returning stroke, when produced upon the large scale of nature, where the elastic electrical pressure is so powerful.

To these arguments adduced by his lordship for the existence and strength of the electrical returning stroke, we shall add an account of some experiments published Lightning in the Gentleman's Magazine for 1785. They were made with an insulated rod of iron of considerable length, rising some feet higher than a common conductor placed at the other end of the house. A set of bells were affixed to the former, which in a thunderstorm, even when the thunder was four or five miles distant, were rung by the electricity of the atmosphere; but whenever a flash of lightning burst from the cloud, even though at the distance just mentioned, the same flash, according to our author, passed through the conductor also, and the bells ceased to ring sometimes for several seconds; then they began again, and continued to ring till they were stopped by another flash. This flash which passed through the conductor was undoubtedly what earl Stanhope calls the returning stroke; of which we must now give some explanation: And in considering the whole doctrine of that stroke, together with the particular explanation laid down by his lordship, the following observations naturally occur.

1. In the experiments made by his lordship to demonstrate the existence of the returning stroke, there is a deception, of which the reviewers take notice, viz., that the man touches a large prime conductor, which, by the operation of the machine, becomes negatively electrified as well as himself. Hence when the discharge is made, all the fire returning to that conductor must pass through his body as well as that of which his body itself is supposed to be deprived; and this, though no other cause intervened, must nearly double the strength of the shock. To make the experiment more fairly, it would be necessary to take away this second conductor, and let the man only touch the brass ball communicating with the earth.

2. In this experiment there is another deception, not taken notice of by the reviewers, viz., that any body immersed in a positive electrical atmosphere becomes negative. Hence the second conductor, by being applied to the air positively electrified by the machine, becomes almost as strongly negative as if another machine had been applied to it on purpose; and this negative electricity will be the stronger in proportion to the strength of electricity in the air surrounding it. Again, it is well known that a plate of air may be charged by means of two smooth pieces of metal held at a small distance from each other, one of them connected with an electrical machine, and the other with the earth. Now supposing, instead of the usual communication, that a man standing upon an insulating stool, held the lower metallic plate in one hand, and with the other hand touched the earth, or a conductor communicating with it, it is plain, that by touching the upper plate, the electricity acquired by the air between them would be discharged, and that the man would feel what earl Stanhope calls the returning stroke; but which in truth is the shock of a charged electric substance, and would therefore be proportionably pungent. Now, in his lordship's experiments, the two conductors answer exactly to the two metallic plates above mentioned; the air between them receives a charge, and is discharged by the explosion from the prime conductor, because this conductor forms one of the charging plates. It is true, that the round shape of the conductors renders them unfavourable for trying the experiment; and this is one reason why it requires a great power of electricity to make the returning stroke sensible. The thickness of the plate of air interposed betwixt the two conductors is another reason; but this makes no difference as to the principles; for his lordship's experiment is undoubtedly no other than that of the Leyden phial. Were his lordship to use two flat plates instead of round conductors, the deception would then be removed; and we may venture to determine a priori, that the returning stroke would then be not only very severe, but even dangerous, with a very powerful machine and large plates.

3. Though the second conductor were entirely removed, yet there would still be a deception in this experiment, for then the surface of the man's body would act in some measure as one of the metallic plates; so that still the experiment would be on the principles of the Leyden phial, though much weaker than before.

4. In order to make this experiment absolutely without deception, the man should stand upon the ground experiment without touching any thing; and in that case we may properly venture to affirm, that he would feel no returning shock. His being insulated varies the nature of the experiment entirely, as will easily be understood from the following considerations.

Under the article Electricity, we have shown that positive electricity does not consist in an accumulation, nor negative electricity in a deficiency, of the fluid; but that all electric phenomena are to be accounted for from the mere motion of the fluid, and that this motion is always a circulation. We have shown, that in the working of a common machine, the electric fluid comes from the earth; that it is accumulated around the prime conductor; evaporates in the air; and is then silently absorbed by the earth, and reconducted to the machine. Hence, in the charging of a machine which works positively, the earth, and all bodies on its surface, for some way round, are in a negative state; because they are then absorbing the electrical fluid from the atmosphere. That part of the earth indeed directly under the feet of the machine, and perhaps some little way farther, is positive; because it is giving out electricity; but the negative portion will be much more extensive. When the conductor is discharged by a spark, then the circulation ceases in a great measure by the collision of the two opposite streams of electric matter. All bodies on the surface of the earth, then, as far as it was negatively electrified, must receive what his lordship calls the returning stroke: but the electricity being diffused among such a number, and over such a wide extent, it is no wonder that it should be insensible. If, however, we inflate a large conducting body, and then make another part of it communicate with the earth by means of a good conductor, we instantly put it in a situation fit for transmitting more than its share of the electricity of the atmosphere, and reducing it to the state of the inflated rubber of an electrical machine, through which the whole quantity of electricity must pass to the phial held towards it, in order to be charged negatively. In proportion to this quantity transmitted the shock must be, not because the conductor has lost a large share of its natural electricity, but because a large quantity is artificially made to pass through it. We may therefore safely venture to affirm, that, in thunder storms, unless a body transmits more than... Lightning than its natural proportion of electric matter, no shock will be felt; much less can the person be killed.

5. In his explanation of the accident which happened to Lauder, his lordship is reduced to the greatest difficulty, and makes one of the most unphilosophical shifts in the world; no less than that of arranging the clouds of heaven, not according to fact, but according to his own imagination. He supposes the existence of two clouds, one below the other; and ascribes to them various motions and situations, which we have already taken notice of: but who knows whether such clouds ever existed? His Lordship does not pretend that any body ever saw them; and thus he runs into what is termed by logicians a vicious circle: he first affirms data, purposely made to accord with his hypothesis, and then proves the hypothesis from the data.

6. Granting the arrangement of the clouds, and everything that his lordship desires, the main requisite is still wanting, viz., a flash of lightning at a distance to produce the returning stroke. According to him, the distant flash and returning stroke must be simultaneous; but Mr. Brydone mentions no such thing: on the contrary, there had been no flash for some little time before; and the immense velocity of the electric fluid will not allow us to suppose that it would take up the usual time betwixt thunder-claps in travelling five or six miles.

7. His lordship accounts for no lightning being seen at the time of the explosion in a very arbitrary and unnatural manner, by supposing it to have proceeded from a discharge of the one imaginary cloud into the other; and that it was not seen on account of the thicknesses of the lower cloud. A much more natural supposition must be, that it happened below the cart-wheels, but was not seen on account of its being daylight, and the cloud of dust which it raised. The succession of noises, too, indicated a succession of explosions, the flashes of which would be less easily observed than a single large one.

8. It seems altogether impossible, that the return of any quantity of natural electricity into a body should matter that body to pieces. In the present case, the fire entered by a small part of the iron of the wheels, and this part was melted. His lordship does not hesitate to own, that the fusion was a proof that the whole fire belonging to the cart, man, and horses, or at least to the cart and man, had entered by this part of the wheels, and consequently more than naturally belonged to that small part of iron. The same evidence, however, will hold good with regard to every other part. We grant that the fire entered the man's body by his right thigh: this might have therefore been burnt by receiving the fire belonging to the whole body; but it ought then to have quietly diffused itself through the other parts of his body, or at least if any damage had been done, it ought to have been done only to the internal parts. Instead of this, a broad zig-zag line upon his body indicated a vast quantity of electric matter running along the surface without entering the body at all. In like manner, his hat being torn in pieces, indicated a violent explosion of electric matter at his head, where there ought to have been little or no explosion, as none could be wanted there except what the hat had parted with; and it is ridiculous to suppose that bats part with such quantities of electricity as would tear them in pieces by its return. The shivering of the cart, the burning and throwing about of the coals, and all the other circumstances of the case, also point out in the clearest manner, not a quantity of electric matter returning to supply any natural deficiency, but an enormous explosion of that matter from the earth overwhelming and destroying whatever stood in its way. That two explosions were made from the earth is very evident, because there were two holes in it; and the very size of these holes indicates a much greater discharge of electricity than we can reasonably suppose to have been lost by the man, horses, and cart.

We shall now consider the experiment quoted from the correspondent in the Gentleman's Magazine. These, of the influence as well as the accident under consideration, undoubtedly show, that during the time of a thunder-storm, both atmosphere and earth are affected for a very considerable way. With regard to the quantity of this electrical affection, however, though it must undoubtedly be excessive when taken all together, we can by no means agree that it is to taken partially. From an experiment related in the Magazine above quoted, it appears, that the electricity of a violent thunder-storm extends sometimes over a circle of 100 miles diameter. "Electricity (says the author) seldom appeared without a shower; but I was surprised, on the 5th of June 1784, that the bells rang with thin and very high clouds, and without the least appearance of rain, till the next post brought me an account of a violent thunder-storm, and very destructive hail, at a village 50 miles distant." We cannot by any means suppose, that all this space was electrified like a charged phial; otherwise, great as the explosions of lightning are, they would still be much greater. This is evident even in our electrical machines. A single phial may be charged much higher than a battery, as appears by the electrometer; but the battery, though less charged, will have incomparably more power than a single phial. His lordship appears to have deceived himself in this matter, by mistaking the extent of the electrified surface for the quantity of charge in every part of it. The surface of the earth in a thunder-storm is exactly similar to that of a charged conductor. According to the extent of electrified surface, the quantity in spark will be great or small; and just so it is with lightning, for some kinds of it are much more destructive than others. In all cases, however, the quantity of electricity in a particular spot is very inconsiderable. Lightning strikes bodies, not because they are highly electrified, but because they afford a communication betwixt the atmosphere and some place below the surface of the earth. This stroke is the aggregate of the whole electricity contained in a circle of probably many miles in diameter; but the returning stroke, if bodies are in their natural state, can only be in proportion to the quantity of electricity in each substance contained within that space. It is in fact the lightning itself diffused through the earth which makes the returning stroke; and it is impossible that every substance within two or three miles of the explosion can receive the whole flash, or another equal to it. It is only in cases where the quantity of electricity, diffused through a great space, happens to discharge... Lightning itself through a human body or other conducting substance of no great bulk, that the effects upon the latter can be any way considerable. This was undoubtedly the case with the thunder-rod mentioned by the correspondent in the Magazine; for it received either from the atmosphere or from the earth, at the time of every flash, the whole quantity of electricity which had been diffused for a considerable way round. Pointed bodies, we know, draw off electricity very powerfully; in so much that an highly charged jar may be deprived of almost all its power by merely presenting a needle to it. We can be at no loss therefore to understand why a pointed conductor should draw off the electricity from a large portion of the surface of the earth, or from a considerable portion of atmosphere.

We must now, however, inquire into the reason of these appearances of sparks in places at such distance from the explosion of the lightning. To understand this, we must always keep in our eye that principle so fully explained under the article Electricity, viz. that there never is, nor can be, a real deficiency of the electric fluid in any substance or in any place. It is to be considered as an absolute plenum, and of consequence it can have no other motion than a circulatory one. At every discharge of lightning therefore from the clouds into the earth, or from one cloud into another, there must be a return of the same quantity to those clouds which have made the discharge. In the vast extent of electrified surface, some part of these returns must undoubtedly be made at great distances from the place where the explosion of lightning happens. As long as matters remain in their natural state, the electric matter will return by innumerable passages in such small streams, that no perceptible effect upon any single substance can take place. But if a body be so situated, that a large portion of the electric matter must return through it from the earth, then such body will undoubtedly be more affected by every flash than the rest of the substances around it; and if the communication with the earth be interrupted, a flash of fire will be perceived betwixt the conducting substance and the earth at the time that a flash bursts out from the cloud. The strength of such a flash, however, must by no means be supposed equivalent to that of the main stroke of lightning, unless we could suppose the whole electrical power of the vast circle already mentioned to be discharged through the conductor.

But though this may explain the reason of the explanation sparks or flashes observed in the case of the thunder-rod just mentioned, we cannot from this principle account for the accident which befell the man and horses. There was indeed at that time a very violent emission of electricity from the earth, but no distant flash of lightning happened at the same moment with it, to expel the electricity from the earth. It appears therefore, that the electricity laid in this case been accumulating in the earth itself, in a manner similar to that which produces earthquakes; and which is fully explained under that article. The thunder-storm was the natural means employed to supply that part of the earth with electricity, which was in the state of charging; and the moment that the quantity thus supplied was thrown back, all signs of electricity must cease, as much as when that thrown in upon one side of a Leyden phial is again thrown off. Hence, when the flash burst out of the earth, and killed the man and horses, that portion of earth which absorbed the electricity till then, required it no longer; and of consequence the thunder-storm occasioned by this absorption naturally ceased.

That this disposition to an earthquake did really prevail in the earth at that time, is evident from the tremor which Mr Bell felt on the ground when walking in his garden. The stroke which the woman received on the foot, the death of the lamb, and no doubt many similar circumstances, concurred to show that there was an attempt to restore the equilibrium from the earth, as has been already related. The same disposition to an earthquake, however, was afterwards renewed; and on the 11th of August that same year, a smart shock of an earthquake did actually take place, as Mr Brydone informs us in the same paper.

Besides the different kinds of lightning already treated of, it is by no means uncommon to see flashes unattended by any report. These are always of the fleet kind; they happen very frequently in windy weather when the sky is clear; and likewise when the sky is cloudy, immediately before a fall of rain or snow. The general reason of these appears to be, that the electric fluid is the medium by which the vapours are suspended in the atmosphere; and of consequence, every separation of vapour, whether as rain, snow, or hail, must be attended with what is called a discharge of electrical matter. The reason why this kind of lightning is never attended with any report is, that there is no particular object against which the force of the flash is directed; but it dissipates itself among the innumerable conducting bodies with which the atmosphere always abounds. It is, however, in a manner impossible to explain the various ways in which this subtle fluid acts. We know not, for instance, in what state it is when acting as a medium of connection betwixt the air and vapour, nor in what its discharge into other parts of the atmosphere properly consists. At any rate, we see that a flash of lightning, however limited its extent may appear to us, diffuses its effects over a great space of atmosphere; for after one of these silent flashes, it is no uncommon thing to observe the sky to become obscure though it had been quite serene before; or, if it had been cloudy, to see rain or snow begin to fall in a very few minutes. It is probable indeed, that there is no change whatever that can take place in the atmosphere but by means of electricity; and there is great reason to believe, that the silent discharges of this fluid from one part of the atmosphere to another, many of which are totally invisible, ultimately occasion the whole of the phenomena of Meteorology. See that article.

Various parts of his Lordship's Treatise on Electricity, besides those already quoted, tend to prove for convenience to those who terminate in a ball, or rounded end. Towards the end of the performance, the author discusses this matter very particularly; and enumerates the 'necessary requisites' in erecting them, in number 11; to every one of which we readily As this matter is of a popular nature, and on a subject generally interesting, we shall transcribe this list; adding a short explanation to particular articles.

These requisites (says the author) are 11 in number.

1stly, That the rod be made of such substances as are, in their nature, the best conductors of electricity.

2ndly, That the rod be uninterrupted, and perfectly continuous. This is a very material circumstance. One entire piece of metal cannot perhaps be had; but it is not sufficient that the rods, of which the conductor consists, be sensibly in contact; they should be pressed into actual contact by means of nuts and screws, with a thin piece of sheet-lead between the shoulders of the joints.

3rdly, That it be of a sufficient thickness. A copper rod half an inch square, or an iron rod one inch square, or one of lead two inches square, are thought fully sufficient by the author.

4thly, That it be perfectly connected with the common stock. That is, it should be carried deep into the earth, which is frequently dry near the surface; and then continued in a horizontal direction, so as to have the farther extremity dipped, should this be practicable, into water, at the distance of 10 yards or more from the foundation.

5thly, That the upper extremity of the rod be as acutely pointed as possible. This termination should be of copper; or rather a very fine and exceedingly acute needle of gold should be employed, which will not materially add to the expense.

6thly, That it be very finely tapered; so that the upper extremity may be a cone, the diameter of the base of which may bear an extremely small proportion to its height; for instance, that of one to forty.

7thly, That it be extremely prominent; that is, 8, 10, or 15 feet at least above the highest parts of the building. The author lays great stress on this circumstance; in consequence of the law above-mentioned, deduced by him from his experiments, relating to electric atmospheres. According to this law, the density of an electric atmosphere (the negative atmosphere, for instance, of the roof of a house, &c., while a positively charged cloud hangs over it) diminishes in the inverse ratio of the square of the distance from the surface of the body to which that atmosphere belongs. Accordingly, if the rod project 12 feet into this atmosphere, it will reach to a part of it four times less dense than if the rod projected only to half that distance, or six feet; and to a part one hundred and forty-four times rarer, than if it projected only one foot.

8thly, That each rod be carried, in the shortest convenient direction, from the point at its upper end, to the common stock.

9thly, That there be neither large nor prominent bodies of metal upon the top of the building proposed to be secured, but such as are connected with the conductor, by some proper metallic communication.

10thly, That there be a sufficient number of high and pointed rods. On edifices of great importance, especially magazines of gun-powder, the author thinks these ought never to be above 40 or 50 feet asunder.

11thly, That every part of the rods be very substantially erected.

The author declares that he has 'never been able to hear of a single instance, nor does he believe that any one can be produced, of an high, tapering, and acutely pointed metallic conductor, having ever, in any country, been struck by lightning; if it had all the necessary requisites abovementioned, especially the second and fourth.'

On the whole, it seems to be pretty certain, that both pointed and knopped metallic conductors have the power of preserving any body placed at a small distance from them from being struck by lightning. This they do, not because they can attract the lightning far out of its way, but because the resistance to its passage is always least on that side where they are; and as pointed conductors diminish the resistance more considerably than blunt ones, they seem in all cases to be preferable. It appears, however, that a single conductor, whether blunt or pointed, is not capable of securing all the parts of a large building from strokes of lightning; and therefore several of them will be required for this purpose: but to what distance their influence extends, hath not been determined, nor does it seem easily capable of being ascertained.

It now remains only to explain some of the more uncommon appearances and effects of lightning. One thing seems of these is, that it is frequently observed to kill alternately; that is, supposing a number of people standing in a line; if the first person was killed, the second perhaps would be safe; the third would be killed, and the fourth safe; the fifth killed, &c. Effects of this kind are generally produced by the most violently kind of lightning; namely, that which appears in the form of balls, and which are frequently seen to divide themselves into several parts before they strike. If one of these parts of a fire-ball strike a man, another will not strike the person who stands immediately close to him; because there is always a repulsion between bodies electrified the same way. Now, as these parts into which the ball breaks have all the same kind of electricity, it is evident that they must for that reason repel one another; and this repulsion is so strong, that a man may be interposed within the stroke of two of them, without being hurt by either.

The other effect of lightning is mentioned under Why it the article JERUSALEM, where those who attempted sometimes to rebuild the temple had the marks of crosses impressed upon their garments and bodies. This may reasonably be thought to arise from the same cause to of a cross, which the angular appearance of lightning in the air is owing, namely, its violent impetus and velocity, together with the opposition of the atmosphere. A fatal stroke of lightning, sometimes indeed a very considerable one, cannot always enter the substance of terrestrial bodies, even when it touches them, for reasons already given. In this case it runs along their surface, and, as in its motion it is perpetually reflected by the atmosphere, it undoubtedly has the same angular motion which we often perceive in the atmosphere. If in this situation it happens to touch the human skin, or a garment, especially of linen, as being a conductor, it will undoubtedly leave a mark upon it; and this mark being of a zig-zag form, might, in the above instance, have been either taken for the exact form of a cross. Lightning crops by the beholders, or have suggested that idea in relating the story to make it appear more wonderful.

These observations may serve to give some idea of the nature of lightning, and its operations after it appears in its proper form and bursts out from the cloud; but for an account of its original formation, and of the powers by which the clouds are at first electrified, and their electricity kept up notwithstanding many successive discharges of lightning, and the quantity of electric matter continually carried off by the rain, &c. see the article Thunder.

Artificial Lightning. Before the discoveries of Dr Franklin concerning the identity of electricity and lightning, many contrivances were invented in order to represent this terrifying phenomenon in miniature: the corruptions of phosphorus in warm weather, the accension of the vapour of spirit of wine evaporated in a close place, &c. were used in order to support the hypothesis which at that time prevailed; namely, that lightning was formed of some sulphureous, nitrous, or other combustible vapours, floating in long trains in the atmosphere, which by some unaccountable means took fire, and produced all the destructive effects of that phenomenon. These representations, however, are now no more exhibited; and the only true artificial lightning is universally acknowledged to be the discharge of electric matter from bodies in which it is artificially set in motion by our machines.

Lightning was looked upon as sacred both by the Greeks and Romans, and was supposed to be sent to execute vengeance on the earth: Hence persons killed with lightning, being thought hateful to the gods, were buried apart by themselves, lest the ashes of other men should receive pollution from them. Some say they were interred upon the very spot where they died; others will have it that they had no interment, but were suffered to rot where they fell, because it was unlawful for any man to approach the place. For this reason the ground was hedged in, lest any person unawares should contract pollution from it. All places struck with lightning were carefully avoided and fenced round, out of an opinion that Jupiter had either taken offence at them, and fixed upon them the marks of his displeasure, or that he had, by this means, pitched upon them as sacred to himself. The ground thus fenced about was called by the Romans bidentul. Lightning was much observed in augury, and was a good or bad omen, according to the circumstances attending it.