the descent of water from the atmosphere in the form of drops of a considerable size. By this circumstance it is distinguished from dew and fog: in the former of which the drops are so small that they are quite invisible; and in the latter, though their size is larger, they seem to have very little more specific gravity than the atmosphere itself, and may therefore be reckoned hollow spheres rather than drops.

It is universally agreed, that rain is produced by the water previously absorbed by the heat of the sun, or otherwise, from the terraqueous globe, into the atmosphere; but very great difficulties occur when we begin to explain why the water, once so closely united with the atmosphere, begins to separate from it. We cannot ascribe this separation to cold, since rain often takes place in very warm weather; and though we should suppose the condensation owing to the superior cold of the higher regions, yet there is a remarkable fact which will not allow us to have recourse to this supposition. It is certain, that the drops of rain increase in size considerably as they descend. On the top of a hill, for instance, they will be small and inconsiderable, forming only a drizzling shower; but at the bottom of the same hill the drops will be excessively large, descending in an impetuous rain; which shows that the atmosphere is disposed to condense the vapours, and actually does so, as well where it is warm as where it is cold.

For some time the suppositions concerning the cause of rain were exceedingly insufficient and unsatisfactory. It was imagined, that when various congeries of clouds were driven together by the agitation of the winds, they mixed, and run into one body, by which means they were condensed into water. The coldness of the upper parts of the air also was thought to be a great means of collecting and condensing the clouds into water; which, being heavier than the air, must necessarily fall down through it in the form of rain. The reason why it falls in drops, and not in large quantities, was said to be the resistance of the air; whereby being broken, and divided into smaller and smaller parts, it at last arrives to us in small drops. But this hypothesis is entirely contrary to almost all the phenomena: for the weather, when coldest, that is, in the time of severe frosts, is generally the most serene; the most violent rains also happen where there is little or no rain to condense the clouds; and the drops of rain, instead of being divided into smaller and smaller ones as they approach the earth, are plainly increased in size as they descend.

Mr Derham accounted for the precipitation of the drops of rain from the vesicles being full of air, and meeting with an air colder than they contained, the air they contained was of consequence contracted into a smaller space; and consequently the watery shell rendered thicker, and thus specifically heavier, than the common atmosphere. But, under the article Evaporation it has been shown, that the vesicles, if such they are, of vapour, are not filled with air, but with fire, or heat; and consequently, till they part with this latent heat, the vapour cannot be condensed. Now, cold is not always sufficient to effect this, since in the most severe frosts the air is very often serene, and parts with little or none of its vapour for a very considerable time. Neither can we admit the winds to have any considerable agency in this matter, since we find that blowing upon vapour is so far from condensing it, that it unites it more closely with the air, and wind is found to be a great promoter of evaporation.

According to Rohault, the great cause of rain is the heat of the air, which, after continuing for some time near the earth, is raised on high by a wind, and there thawing the snowy villi or flocks of half-frozen vesicula, reduces them to drops; which, coalescing, descend. Here, however, we ought to be informed by what means these vesicles are suspended in their half-frozen state; since the thawing of them can make but little difference in their specific gravity, and it is certain that they ascended through the air not in a frozen but in an aqueous state.

Dr Clarke and others ascribe this descent of the rain rather to an alteration of the atmosphere than of the vesicles; and suppose it to arise from a diminution of the elastic force of the air. This elasticity, which, they say, depends chiefly or wholly upon terrene exhalations, being weakened, the atmosphere sinks under its burden, and the clouds fall. Now, the little vesicles being once upon the descent will continue therein, notwithstanding the increase of resistance they every moment meet with. For, as they all tend to the centre of the earth, the farther they fall, the more coalitions they will make; and the more coalitions, the more matter will there be under the same surface; the surface increasing only as the squares, but the solidity as the cubes; and the more matter under the same surface, the less resistance will there be to the same matter. Thus if the cold, wind, &c. act early enough to precipitate the ascending vehicles before they are arrived at any considerable height, the coals being but few, the drops will be proportionably small; and thus is formed a dew. If the vapors be more copious, and rise a little higher, we have a mist or fog. A little higher still, and they produce a small rain; if they neither meet with cold nor wind, they form a heavy thick dark sky. This hypothesis is equally unsatisfactory with the others; for, granting that the descent and condensation of the vapors are owing to a diminution of the atmosphere's elasticity, by what is this diminution occasioned? To say that it is owing to terrestrial exhalations, is only solving one difficulty by another; since we are totally unacquainted both with the nature and operation of these exhalations. Besides, let us suppose the cause to be what it will, if it acts equally and at once upon all the vapor in the air, then all that vapor must be precipitated at once; and thus, instead of gentle showers continuing for a considerable length of time, we would have the most violent waterspouts, continuing only for a few minutes, or perhaps seconds, which, instead of refreshing the earth, would drown and lay waste everything before them.

Since philosophers have admitted the electric fluid to such a large share in the operations of nature, almost all the natural phenomena have been accounted for by the action of that fluid; and rain, among others, has been reckoned an effect of electricity. But this word, unless it is explained, makes us no wiser than we were before; the phenomena of artificial electricity having been explained on principles which could scarce apply in any degree to the electricity of nature; and therefore all the solution we can obtain of the natural appearances of which we speak comes to this, that rain is occasioned by a moderate electrification, hail and snow by one more violent, and thunder by the most violent of all; but in what manner this electrification is occasioned, hath not yet been explained.—Throughout the various parts of this work where electricity hath been occasionally mentioned, the principles of artificial electricity, laid down in the treatise appropriated to that subject, have been applied to the solution of the phenomena of nature; those which are necessary to be attended to here, are the following.

1. The electric fluid and solar light are the same substance in two different modifications.

2. Electricity is the motion of the fluid when running, or attempting to run, in a continued stream from one place to another: heat is when the fluid has no tendency but to vibrate outwards and inwards to and from a centre; or at least when its streams converge to a point or focus.

3. The fluid acting as electricity, like water, or any other fluid, always tends to the place where there is least resistance.

On these three principles may the phenomena of atmospherical electricity, and the descent of rain by its means, be explained as follows.

1. The light or heat of the sun, acting in that peculiar manner which we call heat, unites itself with the moisture of the earth, and forms it into vapour, which thus becomes specifically lighter than air, and of consequence ascends in the atmosphere to a certain height.

2. Besides the quantity of light which is thus united to the water, and forms it into vapour, a very considerable quantity enters the earth, where it assumes the nature of electric fluid.

3. As the earth is always full of that fluid, every quantity which enters must displace an equal quantity which is already there.

4. This quantity which is displaced must escape either at a distance from the place where the other enters, or very near it.

5. At whatever place a quantity of electric matter escapes, it must electrify the air above that place where it has escaped; and as a considerable quantity of light must always be reflected from the earth into the atmosphere, where it does not combine with the aqueous vapour, we have thence another source of electricity to the air; as this quantity must undoubtedly assume the action of electric fluid, especially after the action of the sun has ceased. Hence the reason why in serene weather the atmospherical electricity is always strongest, and rather more so in the night than in the day.

6. From these considerations, we see an evident reason why there must commonly be a difference between the electricity of the earth, and that of the atmosphere, excepting when an earthquake is about to ensue. The consequence of this must be, that as the action of the solar light continues to bring down the electric matter, and the earth continues to discharge an equal quantity of it into the atmosphere, some part of the atmosphere must at last become overloaded with it, and attempt to throw it back into the earth. This attempt will be vain, until a vent is found for the electricity at some other place; and as soon as this happens, the electrified atmosphere begins to throw off its superfluous electricity, and the earth to receive it. As the atmosphere itself is a bad conductor, and the more so the drier it is, the electric matter attacks the small aqueous particles which are detained in it by means of the latent heat. These, being unable to bear the impetus of the fluid, throw out their latent heat, which easily escapes, and thus makes a kind of vacuum in the electrified part of the atmosphere. The consequences of this are, that the aqueous particles being driven together in large quantity, at last become visible, and the sky is covered with clouds; at the same time a wind blows against these clouds, and, if there is no resistance in the atmosphere, will drive them away.

7. But if the atmosphere all round the cloud is exceedingly electrified, and the earth is in no condition to receive the superfluous fluid excepting in that place which is directly under the cloud; then the whole electricity of the atmosphere for a vast way round will tend to that part only, and the cloud will be electrified to an extreme degree. A wind will now blow against the cloud from all quarters, more and more of the vapour will be extricated from the air by the electric matter, and the cloud will become darker and thicker, at the same time that it is in a manner stationary, as being acted upon by opposite winds; winds; though its size is enlarged with great rapidity by the continual supplies of vapour brought by the winds.

8. The vapours which were formerly suspended invisibly by means of the latent heat, are now suspended visibly by the electric fluid which will not let them fall to the earth, until it is in a condition to receive the electric matter descending with the rain. It is easy to see, however, that thus every thing is prepared for a violent storm of thunder and lightning as well as rain. The surface of the earth becomes electrified from the atmosphere: but when this has continued for some time, a zone of earth considerably below the surface acquires an electricity opposite to that of the clouds and atmosphere; of consequence the electricity in the cloud being violently pressed on all sides will at last burst out towards that zone where the resistance is least, as explained under the article Lightning.—The vapours now having lost that which supported them, will fall down in rain, if there is not a sufficient quantity of electric matter to keep them in the same state in which they were before: but if this happens to be the case, the cloud will instantly be charged again, while little or no rain will fall; and hence very violent thunder sometimes takes place without any rain at all, or such as is quite inconsiderable in quantity.

9. When the electricity is less violent, the rain will descend in vast quantity, especially after every flash of lightning; and great quantities of electric matter will thus be conveyed to the earth, inasmuch that sometimes the drops have been observed to shine as if they were on fire, which has given occasion to the reports of fiery rain have fallen on certain occasions. If the quantity of electric matter is smaller, so that the rain can convey it all gradually to the ground, there will be rain without any thunder; and the greater the quantity of electricity, the more violent will be the rain.

From this account of the causes of rain, we may see the reason why in warm climates the rains are excessive, and for the most part accompanied with thunder; for there the electricity of the atmosphere is immensely greater than it is with us. We may also see why in certain places, according to the situation of mountains, seas, &c. the rains will be greater than in others, and likewise why some parts of the world are exempted from rain altogether; but as a particular discussion of these would necessarily include an explanation of the causes and phenomena of Thunder, we shall for this reason refer the whole to be treated of under that article.

Preternatural Rains. We have numerous accounts, in the historians of our own as well as other countries, of preternatural rains; such as the raining of stones, of dust, of blood, nay, and of living animals, as young frogs, and the like. We are not to doubt the truth of what those who are authors of veracity and credit relates to us of this kind, so far as to suppose that the falling of stones and dust never happened; the whole mistake is, the supposing them to have fallen from the clouds: but as to the blood and frogs, it is very certain that they never fell at all, but the opinion has been a mere deception of the eyes. Men are extremely fond of the marvellous in their relations; but the judicious reader is to examine strictly whatever is reported of this kind, and is not to suffer himself to be deceived.

There are two natural methods by which quantities of stones and dust may fall in certain places, without their having been generated in the clouds or fallen as rain. The one is by means of hurricanes; the wind which we frequently see tearing off the tiles of houses, and carrying them to considerable distances, being equally able to take up a quantity of stones, and drop them again at some other place. But the other, which is much the most powerful, and probably the most usual way, is for the eruptions of volcanoes and burning mountains to toss up, as they frequently do, a vast quantity of stones, ashes, and cinders, to an immense height in the air: and these, being hurried away by the hurricanes and impetuous winds which usually accompany those eruptions, and being in themselves much lighter than common stones as being half calcined, may easily be thus carried to vast distances; and there falling in places where the inhabitants know nothing of the occasion, they cannot but be supposed by the vulgar to fall on them from the clouds. It is well known, that, in the great eruptions of Atna and Vefuvius, showers of ashes, dust, and small cinders, have been seen to obscure the air, and overspread the surface of the sea for a great way, and cover the decks of ships; and this at such a distance, as it should appear scarce conceivable that they should have been carried to: and probably, if the accounts of all the showers of these substances mentioned by authors be collected, they will all be found to have fallen within such distances of volcanoes; and, if compared as to the time of their falling, will be found to correspond in that also with the eruptions of those mountains. We have known instances of the ashes from Vefuvius having been carried thirty, nay, forty leagues, and peculiar accidents may have carried them yet farther. It is not to be supposed that these showers of stones and dust fall for a continuance in the manner of showers of rain, or that the fragments or pieces are as frequent as drops of water; it is sufficient that a number of stones, or a quantity of dust, fall at once on a place, where the inhabitants can have no knowledge of the part from whence they came, and the vulgar will not doubt their dropping from the clouds. Nay, in the canton of Berne in Switzerland, the inhabitants accounted it a miracle that it rained earth and sulphur upon them, at a time that a small volcano terrified them; and even while the wind was so boisterous, and hurricanes so frequent, that they saw almost every moment the dust, sand, and little stones torn up from the surface of the earth in whirlwinds, and carried to a considerable height in the air, they never considered, that both the sulphur thrown up by the volcano, and the dust, &c. carried from their feet must fall soon after somewhere. It is very certain that in some of the terrible storms of large hail, where the hail-stones have been of many inches round, that on breaking them there have been found what people have called stones in their middle; but these observers needed only to have waited the dissolving of one of these hail stones, to have seen the stone in its centre disintegrate, it being only formed of the particles of loose earthy matter, which the water, exhaled by the sun's heat, had taken up in extremely small molecules with with it; and this only having served to give an opake hue to the inner part of the congelation, to which the freezing of the water alone gave the apparent hardness of stone.

The raining of blood has been ever accounted a more terrible sight and a more fatal omen than the other preternatural rains already mentioned. It is very certain that nature forms blood no where but in the vessels of animals, and therefore showers of it from the clouds are by no means to be credited. Those who suppose that what has been taken for blood has been actually seen falling through the air, have had recourse to flying insects for its origin, and suppose it the eggs or dungs of certain butterflies discharged from them as they were high up in the air. But it seems a very wild conjecture, as we know of no butterfly whose excrements, or eggs, are of such a colour, or whose abode is so high, or their flocks so numerous, as to be the occasion of this.

It is most probable that these bloody waters were never seen falling; but that people seeing the standing waters blood-coloured, were assured, from their not knowing how it should else happen, that it had rained blood into them. A very memorable instance of this there was at the Hague in the year 1670. Swammerdam, who relates it, tells us, that one morning the whole town was in an uproar on finding their lakes and ditches full of blood, as they thought; and having been certainly full of water the night before, they agreed it must have rained blood in the night: but a certain physician went down to one of the canals, and taking home a quantity of this blood-coloured water, he examined it by the microscope, and found that the water was water still, and had not at all changed its colour; but that it was full of prodigious swarms of small red animals, all alive, and very nimble in their motions, whose colour and prodigious number gave a red tinge to the whole body of the water they lived in, on a less accurate inspection. The certainty that this was the case, did not however persuade the Hollanders to part with the miracle: they prudently concluded, that the sudden appearance of such a number of animals was as great a prodigy as the raining of blood would have been; and are assured to this day, that this portent foretold the scene of war and destruction which Lewis XIV. afterwards brought into that country, which had before enjoyed 40 years uninterrupted peace.

The animals which thus colour the water of lakes and ponds, are the polices arborecentes of Swammerdam, or the water-fleas with branched horns. These creatures are of a reddish-yellow or flame colour: they live about the sides of ditches, under weeds, and among the mud; and are therefore the least visible, except at a certain time, which is in the end or beginning of June: it is at this time that these little animals leave their recesses to float loose about the water, to meet for the propagation of their species, and by that means become visible in the colour they give the water. This is visible, more or less, in one part or other of almost all standing waters at this season; and it is always at this season that the bloody waters have alarmed the ignorant.

The raining of frogs is a thing not less wonderful in the accounts of authors who love the marvellous, than those of blood or stones; and this is supposed to happen so often, that there are multitudes who pretend to have been eye-witnesses of it. These rains of frogs always happens after very dry seasons, and are much more frequent in the hotter countries than in the cold ones. In Italy they are very frequent; and it is not uncommon to see the streets of Rome (warming both with young frogs and toads in an instant, in a shower of rain); they hopping everywhere between the people's legs as they walk, though there was not the least appearance of them before. Nay, they have been seen to fall through the air down upon the pavements. This seems a strong circumstance in favour of their being rained down from the clouds; but, when strictly examined, it comes to nothing: for these frogs that are seen to fall, are always found dead, lamed, or bruised by the fall, and never hop about as the rest; and they are never seen to fall, except close under the walls of houses, from the roofs and gutters of which they have accidentally slipped down. People, who love to add to strange things yet stranger, affirm that people have had the young frogs fall into their hats in the midst of an open field; but this is idle, and wholly false.

People, who cannot agree to their falling from the clouds, have tried to solve the difficulty of their sudden appearance, by supposing them hatched out of the egg, or spawn, by these rains. Nay, some have supposed them made immediately out of the dust; but there are unanswerable arguments against all these suppositions. Equivocal generation, or the spontaneous production of animals out of dust, is now wholly exploded. The fall from the clouds must destroy and kill these tender and soft-bodied animals: and they cannot be at this time hatched immediately out of eggs; because the young frog does not make its appearance from the egg in this form, but has its hinder legs enveloped in a skin, and is what we call a tadpole; and the young frogs are at least 100 times larger at the time of their appearance, than the egg from which they should be hatched.

It is a certainty, that the frogs, which make their appearance at this time, were hatched and in being long before: but that the dry seasons had injured them, and kept them sluggish in holes, or coverts; and that all the rain does, is the enlivening them, giving new spirits, and calling them forth to seek new habitations, and enjoy the element they were destined in great part to live in. Theophrastus, the greatest of all the naturalists of antiquity, has affirmed the same thing. We find that the error of supposing these creatures to fall from the clouds was as early as that author's time; and also that the truth, in regard to their appearance, was as early known; though, in the ages since, authors have taken care to conceal the truth, and to hand down to us the error. We find this venerable sage, in a fragment of his on the generation of animals which appear on a sudden, bantering the opinion, and asserting that they were hatched and living long before. The world owes, however, to the accurate Signor Redi the great proof of this truth, which Theophrastus only has affirmed: for this gentleman, dissecting some of these new-appearing frogs, found in their stomachs herbs and other half-digested food, and openly showing this to his credulous countrymen. asked them whether they thought that nature, which engendered, according to their opinion, these animals in the clouds, had also been so provident as to engender grass there also for their food and nourishment.

To the raining of frogs we ought to add the raining of grasshoppers and locusts, which have sometimes appeared in prodigious numbers, and devoured the fruits of the earth. There has not been the least pretence for the supposing that these animals descended from the clouds, but that they appeared on a sudden in prodigious numbers. The naturalist, who knows the many accidents attending the eggs of these and other like animals, cannot but know that some seasons will prove particularly favourable to the hatching of them, and the prodigious number of eggs that many insects lay could not but every year bring us such abundance of the young, were they not liable to many accidents, and had not provident nature taken care, as in many plants, to continue the species by a very numerous stock of seeds, of which perhaps not one in five need take root in order to continue an equal number of plants. As it is thus also in regard to insects, it cannot but happen, that if a favourable season encourage the hatching of all those eggs, a very small number of which alone were necessary to continue the species, we must, in such seasons, have a proportionate abundance of them. There appeared about 40 years ago, in London, such a prodigious swarm of the little beetle we call the lady-beetle, that the very posts in the streets were everywhere covered with them. But thanks to the progress of philosophy among us, we had no body to assert that it rained cow-ladies, but contented ourselves with saying that it had been a favourable season for their eggs. The prodigious number of a sort of grub which did vast mischief about the same period among the corn and grass by eating off their roots, might also have been supposed to proceed from its having rained grubs by people fond of making everything a prodigy; but our knowledge in natural history assured us, that these were only the hexapod worms of the common hedge-beetle called the cock-chafers.

The raining of fishes has been a prodigy also much talked of in France, where the streets of a town at some distance from Paris, after a terrible hurricane in the night, which tore up trees, blew down houses, &c., were found in a manner covered with fishes of various sizes. Nobody here made any doubt of these having fallen from the clouds; nor did the affluence of fish, of five or six inches long, being generated in the air, at all startle the people, or shake their belief in the miracle, till they found, upon inquiry, that a very well-stocked fish-pond, which stood on an eminence in the neighbourhood, had been blown dry by the hurricane, and only the great fish left at the bottom of it, all the smaller fry having been tossed into their streets.

Upon the whole, all the supposed marvellous rains have been owing to substances naturally produced on the earth, and either never having been in the air at all, or only carried thither by accident.

In Silesia, after a great dearth of wheat in that country, there happened a violent storm of wind and rain, and the earth was afterwards covered, in many places, with small round seeds. The vulgar cried out that Providence had sent them food, and that it had rained millet: but these were, in reality, only the seeds of a species of veronica, or speed-well, very common in that country; and whose seeds being just ripe at that time, the wind had dislodged them from their capsules, and scattered them about. In our own country, we have histories of rains of this marvellous kind, but all fabulous. It was once said to rain wheats in Wiltshire, and the people were all alarmed at it as a miracle; till Mr Cole showed them, that what they took for wheat was only the seeds or kernels of the berries of ivy, which being then fully ripe, the wind had dislodged from the sides of housetops, and trunks of trees, on which the ivy which produced them crept.

And we even once had a raining of fishes near the coast of Kent in a terrible hurricane, with thunder and lightening. The people who saw small sprats flew about afterwards, would have it that they had fallen from the clouds; but those who considered how far the high winds have been known to carry the sea-water, did not wonder that they should be able to carry small fish with it so small a part of the way.