the art of catching fish. See Angling, Fishing, and Fishing, &c. Emecy.

Chinese Fishing. We venture to give this appellation to some very ingenious contrivances of the people of China for catching fish in their lakes, not only fish, but water-fowl. For the purpose of catching fish they have trained a species of pelican, resembling the common corvus, which they call the Leu-tze, or fishing bird. It is brown, with a white throat, the body whitish beneath, and spotted with brown; the tail is rounded, the irides blue, and the bill yellow. Sir George Staunton, who, when the embassy was proceeding on the southern branch of the great canal, saw these birds employed, tells us, that on a large lake, close to the east side of the canal, are thousands of small boats and rafts, built entirely for this species of fishery. On each boat or raft are ten or a dozen birds, which, at a signal from the owner, plunge into the water; and it is astonishing to see the enormous size of fish with which they return, grasped within their bills. They appeared to be well trained, that it did not require either ring or cord about their throats to prevent them from swallowing any portion of their prey, except what their master was pleased to return to them for encouragement and food. The boat used by these fishermen is of a remarkable light make, and is often carried to the lake, together with the fishing birds, by the men who are there to be supported by it.

The same author saw the fishermen busy on the great lake Wei-chuang-hee; and he gives the following account of a very singular method practised by them for catching the fish of the lake without the aid of birds, net, or of hooks.

To one side of a boat a flat board, painted white, is fixed, at an angle of about 45 degrees, the edge inclining towards the water. On moonlight nights the boat is so placed that the painted board is turned to the moon, from whence the rays of light striking on the whitened surface, give to it the appearance of moving water; on which the fish being tempted to leap as on their element, the boatmen raising with a string the board, turn the fish into the boat.

Water-fowl are much sought after by the Chinese, and are taken upon the same lake by the following ingenious device. Empty jars or gourds are suffered to float about upon the water, that such objects may become familiar to the birds. The fisherman then wades into the lake with one of those empty vessels upon his head, and walks gently towards a bird; and lifting up his arm, draws it down below the surface of the water without any disturbance or giving alarm to the rest, several of whom he treats in the same manner, until he fills the bag he had brought to hold his prey. The contrivance itself is not so singular, as it is that the same exactly should have occurred in the new continent, as Ulloa affirms, to the natives of Carthagena, upon the lake Cienega de Tesias.

FISTULA LACHRYMALIS is a disease which, in all its stages, has been treated of in the article SURGERY, chap. xiv. Encycl. A work, however, has been lately published by James Ware surgeon, in which there is the description of an operation for its cure considerably different from that most commonly used, and which, while it is simple, the author's experience has ascertained to be successful.

In the cure of this disfigurement, which is very troublesome, and not very uncommon, it is a well-known practice to insert a metallic tube in the nasal duct of the lachrymal canal: but the advantage derived from this operation is not at all times lasting. Among other causes of failure, Mr. Ware notices the lodgment of inflamed mucus in the cavity of the tube. To remedy this defect, he recommends the following operation.

"If the disfigurement has not occasioned an aperture in the lachrymal sac, or if this aperture be not situated in a right line with the longitudinal direction of the nasal duct, a puncture should be made into the sac, at a small distance from the internal juncture of the palpebrae, and nearly in a line drawn horizontally from this juncture towards the nose with a spear-pointed lancet. The blunt end of a silver probe, of a size rather smaller than the probes that are commonly used by surgeons, should then be introduced through the wound, and gently, but steadily, pushed on in the direction of the nasal duct, with a force sufficient to overcome the obstruction in this canal, and until there is reason to believe that it has freely entered into the cavity of the nose. The position of the probe, when thus introduced, will be nearly perpendicular; its side will touch the upper edge of the orbit; and the space between its bulbous end in the nose and the wound in the skin will usually be found, in a full-grown person, to be about an inch and a quarter, or an inch and three-eighths. The probe is then to be withdrawn, and a silver stylet, of a size nearly similar to that of the probe, but rather smaller, about an inch and three-eighths in length, with a flat head, like that of a nail, but placed obliquely, that it may fit close on the skin, is to be introduced through the duct, in place of the probe, and to be left constantly in it. For the first day or two after the stylet has been introduced, it is sometimes advisable to wash the eye with a weak salutine lotion, in order to obviate any tendency to inflammation which may have been excited by the operation; but this in general is so slight, that our author has rarely had occasion to use any application to remove it. The stylet should be withdrawn once every day for about a week, and afterwards every second or third day. Some warm water should each time be injected through the duct into the nose, and the instrument be afterwards replaced in the same manner as before. Mr. Ware formerly used to cover the head of the stylet with a piece of diachylon plaster spread on black silk, but has of late obviated the necessity for applying any plaster by blackening the head of the stylet with sealing wax.

"The effect (says he) produced by the stylet, when introduced in the way above mentioned, at first gave me much surprize. It was employed with a view similar to that with which Mr Pott recommends the introduction of a bougie; viz. to open and dilate the nasal duct, and thus to establish a passage, through which the tears might afterwards be conveyed from the eye to the nose. I expected, however, that whilst the stylet continued in the duct the obstruction would remain, and of course that the watering of the eye, and the weakness of the sight, would prove as troublesome as they had been before the instrument was introduced. I did not imagine that any essential benefit could result from the operation until the stylet was removed, and the passage thereby opened. It was an agreeable disappointment to me to find that the amendment was much more expeditious. The watering of the eye almost wholly ceased as soon as the stylet was introduced; and in proportion as the patient amended in this respect, his sight also became more strong and useful. The stylet, therefore, seems to act in a twofold capacity: first, it dilates the obstructed passage; and then, by an attraction somewhat similar to that of a capillary tube, it guides the tears through the duct into the nose.

"The wound that I usually make into the sac, if the suppurative process has not formed a suitable aperture in this part, is no larger than is just sufficient to admit the end of the probe or stylet; and this, in general, in a little time, becomes a fitful orifice, through which the stylet is passed without occasioning the smallest degree of pain. The accumulation of matter in the lachrymal sac, which, previous to the operation, is often copious, usually abates soon after the operation has been performed; and, in about a week or ten days, the treatment of the case becomes so easy, that the patient himself, or some friend or servant who is constantly with him, is fully competent to do the whole that is necessary. It consists solely in withdrawing the stylet two or three times in the week, occasionally injecting some warm water, and then replacing the instrument in the same way in which it was done before.

"It is not easy to ascertain the exact length of time that the stylet should be continued in the duct. Some have worn it many years, and, not finding any inconvenience from the instrument, are still afraid and unwilling to part from it. Others, on the contrary, have disfitted it at the end of about a month or six weeks, and have not had the smallest return of the obstruction afterwards."

The author relates so many successful cases of this operation, that we thought it our duty to record his method in this Supplementary volume of our general repository of arts and sciences; for a successful practice, as well in surgery as in physic, must rest on the basis of experience.

OBlique or SECOND FLANK, or FLANK of the Curtain, is that part of the curtain from whence the face of the opposite battalion can be seen, being contained between the lines rasant and fissant, or the greater and less lines of defence; or the part of the curtain between the flank and the point where the flanchant line of defence terminates.

Covered, Low, or Retired Flank, is the platform of the casemate, which lies hid in the bastion, and is otherwise called the orillon.

Flanchant Flank, is that from whence a cannon playing, fires directly on the face of the opposite bastion.

Rafant or Razant Flank, is the point from whence the line of defence begins, from the conjunction of which with the curtain the shot only rafeth the face of the next bastion, which happens when the face cannot be discovered but from the flank alone.

FLIE or Fix, that part of the mariner's compass on which the thirty-two points of the wind are drawn, and over which the needle is placed, and fastened underneath.

FLOATING Bodies are such as swim on the surface of a fluid, of which the most important are ships and all kinds of vessels employed in war and in commerce. Every seaman knows of how much consequence it is to determine the stability of such vessels, and the positions which they assume when they float freely and at rest on the water. To accomplish this, it is necessary to state the principles on which that stability and their positions depend; and this has been done with so much ingenuity and science by GEORGE Atwood, Esq; F. R. S. in the Philosophical Transactions for the year 1796, that we are persuaded a large class of our readers will thank us for inserting an abstract of his memoir in this place.

A floating body is pressed downwards by its own weight in a vertical line that passes through its centre of gravity; and it is sustained by the upward pressure of a fluid, acting in a vertical line that passes through the centre of gravity of the immersed part; and unless these two lines be coincident, so that the two centres of gravity may be in the same vertical line, the solid will revolve on an axis, till it gains a position in which the equilibrium of floating will be permanent. Hence it appears that it is necessary, in the first place, to ascertain the proportion of the part immersed to the whole; for which purpose the specific gravity of the floating body must be known; and then it must be determined, by geometrical or analytical methods, in what positions the solid can be placed on the surface of the fluid, so that the two centres of gravity already mentioned may be in the same vertical line when a given part of the solid is immersed under the surface of the fluid. When these preliminaries are settled, something still remains to be done. Positions may be assumed in which the circumstances just recited concur, and yet the solid will assume some other position in which it will permanently float. If a cylinder, e.g., having its specific gravity to that of the fluid on which it floats as 3 to 4; and its axis to the diameter of the base as 2 to 1, be placed on the fluid with its axis vertical, it will sink to a depth equal to a diameter and a half of the base; and while its axis is preserved in a vertical position by external force, the centres of gravity of the whole solid and of the immersed part will remain in the same vertical line; but when the external force that sustained it is removed, it will decline from its upright position, and will permanently float with its axis horizontal. If the axis be supposed to be half of the diameter of the base, and be placed vertically, the solid will sink to the depth of three-eighths of its diameter; and in that position it will float permanently. If the axis be made to incline to the vertical line, the solid will change its position until it settles permanently with the axis perpendicular to the horizon.

Whether, therefore, a solid floats permanently, or overflows when placed on the surface of a fluid, so that the centre of gravity of the solid and that of the part immersed shall be in the same vertical line, it is said to be in a position of equilibrium; and of this equilibrium there are three species, viz. the equilibrium of stability, in which the solid floats permanently in a given position; the equilibrium of instability, in which the solid, though the two centres of gravity already mentioned are in the same vertical line, spontaneously overflows, unless supported by external force; and the equilibrium of indifference, or the indifferent equilibrium, in which the solid rests on the fluid indifferent to motion, without tendency to right itself when inclined, or to incline itself farther.

If a solid body floats permanently on the surface of a fluid, and external force be applied to incline it from its position, the resistance opposed to this inclination is termed the stability of floating. Among various floating bodies, some lose their quiescent position, and some gain it, after it has been interrupted, with greater facility and force than others.

Some ships at sea (e.g.) yield to a given impulse of the wind, and suffer a greater inclination from the perpendicular than others. As this resistance to heeling or pitching, duly regulated, has been deemed of importance in the construction of vessels, several eminent mathematicians have investigated rules for determining the stability of ships from their known dimensions and weight, without recurring to actual trial. To this class we may refer Bouguer, Euler, Fred. Chapman, and others; who have laid down theorems for this purpose, founded on a supposition that the inclinations of ships from their quiescent positions are evanescent, or, in a practical sense, very small.

"But ships at sea (says our ingenious author) are known to heel through angles of 10°, 20°, or even 30°, and therefore a doubt may arise how far the rules demonstrated on the express condition that the angles of inclination are of evanescent magnitude, should be admitted as practically applicable in cases where the inclinations are so great."—"If we admit that the theory of statics can be applied with any effect to the practice of naval architecture, it seems to be necessary that the rules, investigated for determining the stability of vessels, should be extended to those cases in which the angles of inclination are of any magnitude likely to occur in the practice of navigation."

A solid body placed on the surface of a lighter fluid, at the depth corresponding to the relative gravities, cannot change its position by the combined actions of its weight and the pressure of the fluid, except by revolving on some horizontal axis which passes through the centre of gravity; but as many axes may be drawn through this point of the floating body in a direction parallel to the horizon, and the motion of the solid respects one axis only, this axis must be determined by the figure of the body and the particular nature of the case. When this axis of motion, as it is called, is de- Floating: determined, and the specific gravity of the solid is known; "the positions of permanent floating will be obtained, first by finding the several positions of equilibrium through which the solid may be conceived to pass, while it revolves round the axis of motion; and secondly, by determining in which of those positions the equilibrium is permanent, and in which of them it is momentary and unstable."

Such as we have now briefly stated are the general principles, on which are founded Mr Atwood's investigations for determining the positions assumed by homogeneous bodies, floating on a fluid surface; and also for determining the stability of ships and of other floating bodies. We cannot farther accompany him in his elucidation of them, in the problems to the solution of which they lead, and in the important practical purposes of naval architecture to which they are referred. The whole paper, comprehending no less than 85 pages, is curious and valuable; it abounds with analytical and geometrical disquisitions of the most elaborate kind; and it serves to enlarge our acquaintance with a subject that is not only highly interesting to the speculative mathematician, but extremely useful in its practical application.

With this latter view, the author seems to have directed his attention to the various objects of inquiry which this article comprehends. They are such as intimately relate to the theory of naval architecture, so far as it depends on the pure laws of mechanics, and they contribute to extend and improve this theory. The union of those principles that are deduced from the laws of motion, with the knowledge which is derived from observation and experience, cannot fail to establish the art of constructing vessels on its true basis, and gradually to lead to further improvements of the greatest importance and utility. To this purpose, the author observes, that

"If the proportions and dimensions adopted in the construction of individual vessels are obtained by exact geometrical mensurations, and calculations founded on them, and observations are made on the performance of these vessels at sea; experiments of this kind, sufficiently diversified and extended, seem to be the proper grounds on which theory may be effectually applied in developing and reducing to system those intricate, subtil, and hitherto unperceived causes, which contribute to impart the greatest degree of excellence to vessels of every species and description. Since naval architecture is reckoned amongst the practical branches of science, every voyage may be considered as an experiment, or rather as a series of experiments, from which useful truths are to be inferred towards perfecting the art of constructing vessels; but inferences of this kind, consistently with the preceding remark, cannot well be obtained, except by acquiring a perfect knowledge of all the proportions and dimensions of each part of the ship; and secondly, by making and recording sufficiently numerous observations on the qualities of the vessel, in all the varieties of situation to which a ship is usually liable in the practice of navigation."

In the valuable miscellany entitled the Philosophical Magazine, there is a paper on this subject by Mr John George English, teacher of mathematics and mechanical philosophy; which, as it is not long, and is easily understood, we shall take the liberty to transcribe.

"However operose and difficult the calculations necessary to determine the stability of nautical vessels may, in some cases, be, yet they all depend, says this author, upon the four following simple and obvious theorems, accompanied with other well-known stereometrical and platrical principles.

"Theorem 1. Every floating body displaces a quantity of the fluid in which it floats, equal to its own weight; and consequently, the specific gravity of the fluid will be to that of the floating body, as the magnitude of the whole is to that of the part immersed.

"Theorem 2. Every floating body is impelled downward by its own essential power, acting in the direction of a vertical line passing through the centre of gravity of the whole; and is impelled upward by the reaction of a vertical line passing through the centre of gravity of the part immersed; therefore, unless these two lines are coincident, the floating body thus impelled must revolve round an axis, either in motion or at rest, until the equilibrium is restored.

"Theorem 3. If by any power whatever a vessel be deflected from an upright position, the perpendicular distance between two vertical lines passing through the centres of gravity of the whole, and of the part immersed respectively, will be as the stability of the vessel, and which will be positive, nothing, or negative, according as the metacentre is above, coincident with, or below, the centre of gravity of the vessel.

"Theorem 4. The common centre of gravity of any system of bodies being given in position, if any one of these bodies be moved from one part of the system to another, the corresponding motion of the common centre of gravity, estimated in any given direction, will be to that of the aforementioned body, estimated in the same direction, as the weight of the body moved is to that of the whole system.

"From whence it is evident, that in order to ascertain the stability of any vessel, the position of the centres of gravity of the whole, and of the part immersed, must be determined; with which, and the dimensions of the vessel, the line of floatation, and angle of deflection, the stability or power either to right itself or overturn, may be found.

"In ships of war and merchandise, the calculations necessary for this purpose become unavoidably very operose and troublesome; but they may be much facilitated by the experimental method pointed out in the New Transactions of the Swedish Academy of Sciences, first quarter of the year 1787, page 48.

"In river and canal boats, the regularity and simplicity of the form of the vessel itself, together with the compact disposition and homogeneous quality of the burden, render that method for them unnecessary, and make the requisite calculations become very easy. Vessels of this kind are generally of the same transverse section throughout their whole length, except a small part in prow and stern, formed by segments of circles or other simple curves; therefore a length may easily be assigned such, that any of the transverse sections being multiplied thereby, the product will be equal to the whole solidity of the vessel. The form of the section ABCD is for the most part either rectangular, as in fig. 1., trapezoidal as in fig. 2., or mixtilinear..." tilinear as in fig. 3, in all which MM represents the line of floatation when upright, and EF that when inclined at any angle MXE; also G represents the centre of gravity of the whole vessel, and R that of the part immersed.

If the vessel be loaded quite up to the line AB, and the specific gravity of the boat and burden be the same, then the point G is simply the centre of gravity of the section ABCD; but if not, the centres of gravity of the boat and burden must be found separately, and reduced to one by the common method, namely, by dividing the sum of the moments by the sum of weights, or areas, which in this case are as the weights. The point R is always the centre of gravity of the section MMCD, which, if consisting of different figures, must also be found by dividing the sum of the moments by the sum of the weights as common. These two points being found, the next thing necessary is to determine the area of the two equal triangles MXE, MXF, their centres of gravity o, o, and the perpendicular projected distance n n of these points on the water line EF. This being done, through R and parallel to EF draw RT—a fourth proportional to the whole area MMCD, either triangle MXE or MXF, and the distance n n; through T, and at right angles to RT or EF, draw TS meeting the vertical axis of the vessel in S the metacentre; also through the points G, B, and parallel to ST, draw NGW and BV; moreover through S, and parallel to EF, draw WSV, meeting the two former in V and W; then SW is as the stability of the vessel, which will be positive, nothing, or negative, according as the point S is above, coincident with, or below, the point G. If now we suppose W to represent the weight of the whole vessel and burden (which will be equal to the section MMCD multiplied by the length of the vessel), and P to represent the required weight applied at the gunwale B to sustain the vessel at the given angle of inclination; we shall always have this proportion: as VS : SW : : W : P; which proportion is general, whether SW be positive or negative; it must only in the latter case be supposed to act upward to prevent an overturn.

In the rectangular vessel, of given weight and dimensions, the whole process is so evident, that any farther explanation would be unnecessary. In the trapezoidal vessel, after having found the points G and R, let AD, BC be produced until they meet in K. Then, since the two sections MMCD, EFDC are equal, the two triangles MMK, EFK are also equal; and therefore the rectangle EK × KF = KM × KM = KM²; and since the angle of inclination is supposed to be known, the angles at E and F are given. Consequently, if a mean proportional be found between the sines of the angles at E and F, we shall have the following proportions:

As the mean proportional thus found: fine ∠E : : KM : KP, and as the said mean proportional: fine ∠F : : KM : KE; therefore ME, MF become known; from whence the area of either triangle MXE or MXF, the distance n n, and all the other requisites, may be found.

In the mixtilinear section, let AB = 9 feet = 108 inches, the whole depth = 6 feet = 72 inches, and the altitude of MM the line of floatation 4 feet or 48 inches; also let the two curvilinear parts be circular quadrants of two feet, or 24 inches radius each. Then placing the area of the two quadrants = 947808 square inches, and the distance of their centres of gravity from the bottom = 138177 inches very nearly; also the area of the included rectangle abie = 1440 square inches, and the altitude of its centre of gravity 12 inches; in like manner, the area of the rectangle ABA d will be found = 5184 square inches, and the altitude of its centre of gravity 48 inches; therefore we shall have

\[ \begin{align*} \text{Momentum of } & \quad 947808 \times 138177 = 125019866016 \\ \text{Moment of the } & \quad 1440 \times 12 = 17280 \\ \text{Moment of the } & \quad 5184 \times 48 = 248832 \\ \end{align*} \]

Now the sum of the moments, divided by the sum of the areas, will give \( \frac{2786139866016}{75287808} = 37006 \) inches, the altitude of G, the centre of gravity of the section ABCD above the bottom. In like manner, the altitude of R, the centre of gravity of the section MMCD, will be found to be equal \( \frac{1230939866016}{49367808} = 24934 \) inches; and consequently their difference, or the value of GR = 12072 inches, will be found.

Suppose the vessel to heel 15°, and we shall have the following proportion; namely, As radius : tangent of 15° : : MX = 54 inches = 14469 inches = ME or MF; and consequently the area of either triangle MXE or MXF = 390663 square inches. Therefore, by theorem 4th, as 49367808 : 390663 :: 72 = n n = \( \frac{1}{2} \) AB = 56975 inches = RT; and again, as radius of 15° : : 12072 = GR = 31245 inches = RN; consequently RT—RN = 56975—31245 = 2573 inches = SW, the stability required.

Moreover, as the sine of 15° : radius : : 56975 = RT : 22013 = RS, to which, if we add 24934, the altitude of the point R, we shall have 46947 for the height of the metacentre, which taken from 74, the whole altitude, there remains 25053; from which, and the half width = 54 inches, the distance BS is found = 59529 inches very nearly, and the angle SBV = 80°—6°—42°; from whence SV = 58645 inches.

Again: Let us suppose the mean length of the vessel to be 40 feet, or 480 inches, and we shall have the weight of the whole vessel equal to the area of the section MMCD = 49367808 multiplied by 480 = 2369634784 cubic inches of water, which weighs exactly 85708 pounds avoirdupois, allowing the cubic foot to weigh 62½ pounds.

And finally, as SV : SW (i.e.) as 58645 : 2573 : : 85708 : 3760 + , the weight on the gunwale which will sustain the vessel at the given inclination. Therefore a vessel of the above dimensions, and weighing 38 tons, 5 cwt. 28 lbs. will require a weight of 1 ton, 13 cwt. 64 lbs. to make her incline 15°.

In this example, the deflecting power has been supposed to act perpendicularly on the gunwale at B; but if the vessel is navigated by sails, the centre velocity must be found; with which, and the angle of deflection, the projected distance thereof on the line SV may be obtained; and then the power, calculated as above, necessary. necessary to be applied at the projected point, will be that part of the wind's force which causes the vessel to heel. And conversely, if the weight and dimensions of the vessel, the area and altitude of the sails, the direction and velocity of the wind be given, the angle of deflection may be found."