which terminated in an iron point at the top. This point was put into the end of a small tube of Indian paper, made somewhat in the form of a cartridge, about one inch and a quarter long, and about two-tenths of an inch in diameter. When this cartridge was filled with common gunpowder (unbruifed) the wire of communication with the well' (i. e. the earth) was then fastened to the bottom of the brafs ftem. Being fo circumftanced, and whilft the charge in the great cylinder and wire was continually kept up by the motion of the wheel, the top of the cartridge was brought fo near to the drums as frequently to touch the metal. In this fituation, a small faint luminous ftream was obferved between the top of the cartridge and the metal drum. Sometimes this ftream would fet fire to the gunpowder at the inftant of the application; at others it would require half a minute or more before it took effect. But this difference in time might probably arise from fome difference in the circumftances; for any the leaft moisture in the filk lines, the powder, or in the paper itfelf, was unfavourable to the experiment.' This new method of firing gunpowder, by a luminous ftream ❝ of the matter of lightning, furely merits the most serious attention; and more especially in those cafes where pointed conductors are fixed to fecure magazines of gunpowder from fuch accidents.'-Tinder was ftill more readily fired by the electric blast. Inftead of giving any opinion of our own on the Author's experiments, and deductions from them; it will be more fatif factory to our Readers if we give that of the Committee appointed by the Royal Society, to confider of the most effectual method of fecuring the powder magazines at Purfleet against the effects of lightning, in compliance with the request of the Board of Ordnance. The Committee, among other things, declare, that having attentively examined the experiments and obfervations of Mr. Wilson, and having maturely confidered the fubject at large, it is their opinion that it is very improbable that the powder magazines, guarded in the manner in which they are at present, that is, with elevated pointed conductors, fhould receive any damage from lightning. They even recommend to the Board of Ordnance the erection of feveral additional rods, as acutely pointed as poffible, on the roofs and fome other parts of each of the magazines; and, for the fake of greater fecurity, they propofe that the intire roofs and the tops of the end walls fhould be covered with lead connected with the faid rods. They propose these and other directions, under a perfuafion that elevated rods are preferable to low conductors terminated in rounded ends, knobs, or balls of metal ;'-and that the experiments and reafons, made made and alleged to the contrary by Mr. Wilson, are inconclufive.'-Thefe opinions and directions have the respectable fanction of Sir John Pringle, Dr. Watson, the Hon. H. Cavendish, Mr. Henly, Dr. Horfley, Mr. Lane, Lord Mahon, Mr. Nairne, and Dr. Priestley. Article 10. An Account of fome electrical Experiments. By Mr. William Swift, in a Letter to John Glen King, D. D. F. R. S. There may be much ingenuity and contrivance in the plan and conduct of thefe experiments; but they are related in fo obfcure a manner, that we can collect nothing more from the moft diligent perufal of them, than that the contriver and relator of them is not a Wilfonian, or Big-Endian. Though we, too, are Little-Endians, we can draw no confequences from the dark account which the Author has given of his experiments. MATHEMATICAL PAPERS. Article 3. The Force of fired Gunpowder, and the initial Velocities of Cannon-balls, determined by Experiments, &c. By Mr. Charles Hutton, of the Military Academy at Woolwich. This valuable paper contains an account of several sets of experiments made with a view to determine the actual velocities with which balls are impelled from given pieces of cannon, when fired with given charges of powder. The late ingenious Mr. Robins firft difcovered and practifed the fimple and excellent method, which was adopted by Mr. Hutton in this investigation, with material improvements. This method confifts in reducing the immenfe velocity with which a ball iffues from a cannon, to a smaller velocity produced by caufing it to strike against a heavy body, fuch as a large block of wood, fwinging in the manner of a pendulum. The ball being lodged in the block, the two bodies proceed together, after the fhock, with a velocity which bears the fame ratio to the original velocity of the ball alone, that the weight of the ball has to that of the ball and block united. This velocity, thus reduced from 1000 to perhaps 2 or 3 feet, is eafily measured by obferving the magnitude of the arch, or rather the chord of the arch, defcribed by the pendulum; and this is afcertained by fixing a graduated tape or ribbon to the bottom of the pendulum; which, by the motion of the latter, is drawn through a little machine which gives it a moderate degree of friction. Mr. Robins made his experiments with only musket balls of about an ounce weight, and an apparatus of a proportional fize. The prefent were made with cannon balls, from one to near three pounds weight, and an appropriate apparatus. They appear to have been executed with great care and accuracy; and their refults lead to conclufions of confiderable importance, both to the theorist and the practical artillerist. Article Article 16. On the Arithmetic of impoffible Quantities. By the Rev. John Playfair, A. M. In this paper the Author explains the grounds of those obfcurities and paradoxes, from which Geometry is free, but which have been introduced into Algebra; particularly with respect to the doctrine of negative quantities and its confequences. He obferves that, in geometry, every magnitude is represented by one of the fame kind; lines are reprefented by a line, and angles by an angle: whereas, in algebra, every magnitude is denoted by an artificial fymbol, to which it has no refemblance; and the magnitude itself is liable fometimes to be neglected, while the fymbol becomes the fole object of attention, after the connection between them no longer exifts. Accordingly, the conclufions of the analyft, which hold true only with refpect to the symbols, being transferred to the quantities themselves, obfcurity and paradox neceffarily enfue. The Author exemplifies thete obfervations by confidering the nature of imaginary expreffions, and the different ufes to which they have been applied. Article 17. Reflections on the Communication of Motion by Impact and Gravity. By the Rev. Ifaac Milner. M. A. &c. The Author of this paper endeavours to point out, and distinguifh, what is real from what is verbal, in the long agitated queftion concerning the vires viva, or the forces of bodies in motion; from a ferious perfuafion that the laws by which motion is communicated are ftill very materially mistaken by fenfible perfons;'- and that the right understanding of thefe laws is of the laft importance in practice:' as the good or bad fuccefs of fome very expenfive projects has depended upon it. His design in this paper is to difcriminate between the real and the merely verbal part of this ancient controverfy; and to point out to the controvertifts the grounds of their mutual mistakes and misapprehenfions; which he exemplifies in feveral inftances. Article 18. Obfervations on the Limits of Algebraical Equations; and a general Demonftration of Des Cartes's Rule for finding their Number of Affirmative and Negative Roots. By the fame. MISCELLANEOUS PAPERS. Article 2. Of the Heat, c. of Animals and Vegetables. By Mr. John Hunter, F. R. S. We fhall not, for many reafons, attempt to give any abstract of the numerous experiments related in this paper. They are indeed too complicated to admit of abridgment: and with refpect to those relating to the Author's trials on living animals,-the unfortunate dormice, in particular, who were the fubjects of his calorific and frigoric tortures,--we respect the fenfibility of our Readers, and our own, too ftrongly, even to dwell a moment on the fubject. We have repeatedly, and, we hope, not quite unavailingly, unavailingly, born our teftimony against the studied cruelties of phyfiologifts; particularly in our 42d Vol. March 1770, page 197; our 51ft Vol. September 1774, page 229; and our 55th Vol. Auguft 1776, page 120; to which we refer our Readers, and particularly the Author. Such of his experiments as are not liable to this objection we recommend to the Reader's perufal; though we think great uncertainty must attend the thermometrical observations made on fuch large bodies as trees. There is fome power, or, we should rather perhaps fay, fome circumftances in the economy of living vegetables, by which their juices are fo far protected from the action of very intenfe cold, as not to be frozen by it; though the fame juices, when they are no longer contained in their proper canals, will be frozen in the temperature of 31 or 32 degrees. The juices of the fpruce fir, juniper, &c. are not affected, in countries where the thermometer falls many degrees below o; and where the feet and noses of the inhabitants are frequently frozen. When the tree however is killed, in confequence of an extraordinary increase of cold, its fap or juices freeze; and by their expansion, in the state of ice, split the tree, with a great noise, into a confiderable number of pieces. The numerous experiments which the Author has made on this fubject, and here relates, have not yet enabled him to folve this difficulty. Article 8. An improved Method of Tanning Leather. By David Macbride, M. D. The great advantages which the most useful and neceffary arts may derive from the lights furnished by the experimental Philofopher, and particularly the Chemift, are well exemplified in the paper before us. Their progrefs would be ftill more rapid, did the philofopher poffefs the practical knowledge of the artist; or if the two characters were united in the fame perfon:-a combination which feldom happens. The Author was led to the discovery of this improved method of tanning leather, in confequence of the experiments which he formerly made on the diffolvent power of calcareous earths deprived of their fixed air, or quicklime (erroneously printed quickfilver at page 119 of this article), which were published in his Experimental Effays. One of the Author's principal improvements confifts in ufing lime water, instead of plain common water, in which the bark is to be fteeped, in the preparation of the ooze. This menftruum, he obferves, fo completely exhausts the bark, and makes it go fo much farther than when plain water is used, that a pretty ftrong ooze may be prepared from the tan, or spent bark, which the tanners now confider as completely exhaufted, merely by infufing it afresh in lime water. Another Another advantage is gained, in the Author's method, by the employing oil of vitriol largely diluted with water, instead of the fouring, as it is called, which the Tanners have hitherto, with great trouble and uncertainty, procured from fermented rye or other grain; not knowing that a mere acid was all that was wanted in the procefs. This ufeful fubftitution has already been univerfally adopted by another clafs of artifts, the bleachers of linen; who, however, were not without difficulty prevailed upon to quit their old routine, in preparing a fouring likewife from rye or barley, or four butter-milk; through an ill founded apprehenfion that the vitriolic acid would injure their cloth. The improvements defcribed in this paper are not founded folely on the conjectures of a fpeculative Chemift. After fome trials made on fmall pieces of raw leather, the method was profecuted in a large common tan-yard; and its efficacy has been fully proved by the experience of near ten years, during which time the Author thought proper to keep it fecret. He here bestows his discovery on the public, in a paper of inftructions drawn up in terms fufficiently clear, to enable any intelligent Tanner to avail himself of the improvements described in it. Article 10. An Account of the Island of Sumatra, &c. By Mr. Charles Miller. Among the particulars here related concerning this ifland, we meet with an account of the Battas, a people who live in the interior parts of it, called the Caffia country; and who differ from all the other inhabitants in language, manners, and cuftoms. They eat the prifoners whom they take in war, and hang up their skulls as trophies in their houses. Man's flesh, we are told however, is eaten by them in terrorem, and not as their common food; though they prefer it to all others, and fpeak with peculiar raptures of the foles of the feet and palms of the hands. They expreffed much furprise on being informed that white people did not kill, much less eat, their prisoners.' From this country the greatest part of the Caffia that is fent to Europe is procured. The Author (fon of the late Botanic Gardener) failed in his attempts to difcover the cinnamon tree. The camphire trees abound in this country, and conftitute the common timber in ufe. In these trees the camphire is found native, in a concrete form. It is remarkable that, in this ftate, it is fold to the Chinese, at the price of 250l. or 300 l. per cwt. but these dexterous artifts contrive to furnish us Europeans with it at about a quarter of that price. Article 20. An Effay on Pyrometry and Areometry, and on Phyfical Meafures in general. By John Andrew de Luc, F. R. S. This long article contains many ingenious obfervations, principles, and facts, relative to the conftruction of various phi 4 lofophical |