made concerning the flights and ranges of fhot, except the effects arifing from the refiftance of the medium.' Mr. Hutton then gives a fhort and clear defcription of the nature and general out-line of the method in which the experiments are made, in the following words: • The intention of the experiment is to discover the actual velocity with which a ball iffues from a piece, in the ufual practice of artillery. This velocity is very great; from one thoufand to two thoufand feet in a fecond of time. For conveniently eftimating fo great a velocity, the first thing neceffary is to reduce it, in fome known proportion, to a fmall one. This we may conceive to be effected thus: fuppofe the ball, with a great velocity, to ftrike fome very heavy body, as a large block of wood, from which it will not rebound, fo that they may pro ceed forward together after the ftroke. By this means it is ob. vious, that the original velocity of the ball may be reduced in any proportion, or to any flow velocity which may conveniently be measured, by making the body ftruck to be fufficiently large; for it is well known, that the common velocity, with which the ball and block of wood would move forward after the ftroke, bears to the original velocity of the ball only, the fame ratio which the weight of the ball hath to that of the ball and block together. Thus then velocities of one thoufand feet in a second are easily reduced to thofe of two or three feet only; which small velocity being measured by any convenient means, let the number denoting it be increafed in the proportion of the weight of the ball to the weight of the ball and block together, and the original velocity of the ball itself will thereby be obtained. In thefe experiments, this reduced velocity is rendered very easy to be measured by a very fimple and curious contrivance, which is this: the block of wood, which is truck by the ball, is not left at liberty to move ftraight forward in the direction of the motion of the ball, but it is fufpended, as the weight or bob of a pendulum, by a strong iron ftem, having a horizontal axis at top, on the ends of which it vibrates freely, when ftruck by the ball. The confequence of this fimple contrivance is evi dent: this large ballistic pendulum, after being ftruck by the ball, will be penetrated by it to a fmall depth, and it will then fwing round its axis and defcribe an arch, which will be greater or lefs according to the force of the blow ftruck; and from the fize of the arch defcribed by the vibrating pendulum, the ve locity of any point of the pendulum itfelf can be easily computed; for a body acquires the fame velocity by falling from the fame height, whether it defcend perpendicularly down, or otherwife; therefore the length of the arch defcribed, and of its radius being given, its verfed fine becomes known, which is the height perpendicularly defcended by the corresponding point of the pendulum. The height defcended being thus known, the velocity acquired in falling through that height be comes 327 comes known from the common rules for the defcent of bodies by the force of gravity; and this is the velocity of that point of the pendulum: this velocity of any known point whatever is then to be reduced to the velocity at the center of ofcillation, by the proportion of their radii or diftances from the axis of motion; and the velocity of this center thus obtained, is to be esteemed the velocity of the whole pendulum itfelf; which being now given, that of the ball before the stroke becomes known from the given weights of the ball and pendulum. Thus then the menfuration of the very great velocity of the ball is reduced to the observation of the magnitude of the arch described by the pendulum, in confequence of the blow ftruck. This arch may be measured after various ways: in the following experiments it was afcertained by measuring the length of its chord by means of a piece of tape, or small ribband, the one end of which was faftened to the bottom of the pendulum, and the reft of it made to flide through a small machine contrived for the purpofe; for thus the length of the tape drawn out, was equal to the length of the chord of the arch described by the bottom of the pendulum. This defcription may convey a general idea of the nature and principle of the experiment; but befides the center of of cillation and the weights of the ball and pendulum, the effect of the blow depends alfo on the place of the center of gravity and the point of impact: it will, therefore, be now neceffary to give a more particular defcription of the machine, and of the methods of finding the above mentioned requifites, and then investigate our general rule for determining the velocity of the balls, in all cafes, from them and the chord of the arch of vibration,' These things he then performs in a mafterly way, and brings out a very accurate and much more fimple and easy rule to compute by, than any before given; which he afterwards applies to the neceffary computations of the experiments. Thefe experiments, which are very numerous, being the work of many days, are then detailed in a clear and circumftantial manner, and accompanied with proper obfervations, and deductions drawn from them. To all of which no abftract would here do fufficient juftice. We fhall therefore conclude this important article with a few general inferences drawn from the whole. 1. First, it is made evident by them, that powder fires almoft inftantaneously, feeing that almoft the whole of the charge fires though the time be much diminished. 2. The velocities communicated to balls, or hot, of the fame weight, with different quantities of powder, are nearly in the fub-duplicate ratio of thofe quantities. A very fmall variation, in defect, taking place when the quantities of powder become great. Y 4 " 3. And 3. And when shot of different weights are fired with the fame quantity of powder, the velocities communicated to them are nearly in the reciprocal fub-duplicate ratio of their weights. 4. So that, univerfally, fhot which are of different weights, and impelled by the firing of different quantities of powder, ac quire velocities which are directly as the fquare roots of the quantities of powder, and inversely as the fquare roots of the weights of the shot, nearly. 5. It would therefore be a great improvement in artillery to make use of fhot of a long form, or of heavier matter; for thus the momentum of a hot, when fired with the fame weight of powder, would be increased in the ratio of the fquare root of the weight of the fhot. 6. It would also be an improvement to diminish the wind. age; for by fo doing, one-third or more of the quantity of powe der might be faved. 7. When the improvements mentioned in the last two articles are confidered as both taking-place, it is evident that about half the quantity of powder might be faved, which is a very confiderable object. But important as this faving may be, it feems to be fill exceeded by that of the article of the guns; for thus a fmall gun may be made to have the effect and execution of one of two or three times its fize in the prefent mode, by discharging a fhot of two or three times the weight of its natural ball or round fhot. And thus a fmall fhip might dif charge fhot as heavy as thofe of the greatest now made use of. Finally, as the above experiments exhibit the regulations with regard to the weights of powder and balls, when fired from the fame piece of ordnance, &c. fo by making fimilar experiments with a gun, varied in its length, by cutting off from it a certain part before each courfe of experiments, the effects and general rules for the different lengths of guns may be certainly determined by them. In fhort, the principles on which thefe experiments were made, are fo fruitful in confequences, that, in conjunction with the effects refulting from the refistance of the medium, they feem to be fufficient for anfwering all the enquiries of the fpeculative philofopher, as well as those of the practical artillerit.' Art. IV. A new Cafe in Squinting. By Erafmus Darwin, M. D. F. R S. communicated by Tho. Aftle, Esq. F. R. S. — The fubje&t was a boy of about five years old, and the circumfances as follows: 1. He viewed every object which was prefented to him with but one eye at a time. 2. If the object was prefented on his right fide, he viewed it with his left eye; and if it was prefented on his left fide, he viewed it with his right eye, 3. He turned the pupil of that eye, which was on the fame fide with the object, in fuch a direction that the image of the ob object might fall on that part of the bottom of the eye where the optic nerve enters it. 4. When an object was held directly before him, he turned his head a little to one fide, and obferved it with but one eye, viz. with that moft diftant from the object, turning away the other in the manner above defcribed; and when he became tired with obferving it with that eye, he turned his head the contrary way, and obferved it with the other eye alone, with equal facility; but never turned the axis of both eyes on it at the fame time. fo as 5. He faw letters which were written on bits of paper, to name them with equal eafe, and at equal distances, with one eye as with the other. From these circumftances Dr. Darwin was at first of opinion that there was not any particular defect in one eye more than in the other, which is the common caufe of fquinting, as obferved by M. Buffon and Dr. Reid; and that the disease was fimply a depraved habit of moving his eyes, and might probably be occafioned by the form of a cap or head-drefs, which might have been too prominent on the fides of his face, like bluffs ufed on coach-horfes; and might thence, in early infancy have made it more convenient for the child to view objects placed obliquely with the oppofite eye, till by habit the mufculi adductores were become ftronger, and more ready for motion than their antagonists. In a fupplement to this paper, however, he retra&s this opinion, and subscribes to the general caufe of an original difference in the two eyes above mentioned. He cured the patient in a great meafure by obliging the fight to be directed ftreight forwards, caufing him to wear for a confiderable time, for that purpofe, a gnomon of thin matter, as paper, pafteboard, or brafs, of two or three inches broad, fitted on his nose, so as to prevent him from seeing objects fideways over it. [To be continued. ] A Difcourfe on the Theory of Gunnery. Delivered at the Anniversary Meeting of the Royal Society, November 30, 1778. By Sir John Pringle, Bart. 4to. 15. 6d. Nourfe. THIS HIS is the fixth of those annual difcourfes, that have been printed, of the late very learned prefident of the Royal Society. They are all efteemed elegant and learned compo fitions on the interefting fubje&ts of which they treat and the prefent one, as it is the laft of this kind to be expected from the author, (he having refigned the prefident's chair on his finishing finishing the reading of this difcourfe), fo is it equal, if nok. fuperior, to any of the preceding five. The first paragraph fhews the nature of the general infțitution, as well as the prefent fubject, in these words. 6 Among the feveral experiments communicated to the Society, during the courfe of the preceding year, none feeming fo much to engage your attention, as thofe contained in this paper, intituled, "The force of fired gun-powder, and the initial velocity of cannon-balls, determined by experiments:" with much pleafure therefore I acquaint you, that, on account of the pre-eminence of that communication, your council have judged the author, Mr. Charles Hutton, worthy of the honour of the annual medal, inftituted on the bequeft of fir Godfrey Copley, bart, for raifing a laudable emulation among men of genius, in making experimental inquiries. But, as on former occafions, fo now, your council, waving their privilege of determining the choice, have acted only as a felect number deputed by you, to prepare matters for your final decifion. I come then, on their part, briefly to lay before you the state of the theory of gunnery, from its rife to the time when its true foundation was laid, in order to evince how conducive those experiments may be to the improvement of an art of public concern, as well as to the advancement of natural knowlege, the great object of your inftitution. And if, upon a review of the fubje&t, you fhall entertain no lefs favourable an opinion of Mr. Hutton's performance, than what your council have done, it is their earnest request that you would enhance the value of this prize, by authorizing your prefident to prefent it to our ingenious brother in your name.' Sir John then takes a fhort, but comprehenfive view, of the ancient artillery, or tormenta militaria, from the earliest accounts down to the invention of gun-powder, which is a new epoch in this fcience, and on the ufe of which all the former machines were foon laid afide, as lefs convenient in military affairs. In the fame manner he next traces the gradual improvements in the new mode of this art; evincing that it was not till about 200 years after the ufe of gun powder, that any theory was adopted, which took place first among the Italians, and was drawn from the difcoveries and writings of Galileo; that this theory was afterwards confiderably improved by the French and English; that however till very lately it was a theory purely fpeculative, geometrically drawn from the laws of projection and the defcent of gravity as delivered by the great man last mentioned, according to which every projectile defcribes a parabola in its flight; that as this can only happen to projects made in vacuo, it is now well known to all men of science that the parabolic theory can be of little or no fervice in the re |