The diftinguishing Property of Saltpetre is the prodigious Increase of Inflammability which it produces in all burning Subftances, when mixed with them; altho' alone, and unmixed, it will neither flame nor burn. Now it cannot be reasonably fuppofed, that this Quality of Saltpetre could be long unknown, after the Subftance itself was difcovered; for the accidental dropping of any small Part of it into the Fire, would prove its prodigious explosive Power when mixed with burning Bodies. And this being once obferved, it was thence a very natural Transition to a Compofition of Saltpetre mixed with any inflammable Substance, which would burn more violently than any known before: And our present Gunpowder is only the Improvement and Perfection of such a Mixture.

On this Suppofition then, as Mr. Robins adds, if we knew the Time when Saltpetre first came in Ufe, we might guess when Mixtures refembling our prefent Gunpowder were first invented. Now the most general Opinion on this Head is, that Saltpetre was first discovered, either by the Arabians or the later Greeks, about the middle Ages of our Era.

But, that the firft Invention of Gunpowder, or fome fimilar Compofition, did long precede the Time of Schwartz or Bacon, and may thence be reasonably supposed nearly co-eval with the Knowledge of Saltpetre, appears from Bacon himfelf; for it is not a new Compofition which he proposes, but the Application of an old one to Military Furpofes: And from his Words it plainly appears, that a Mixture of Saltpetre with other Substances was then vulgarly used for the making of recreative Fire-works.

Mr. Robins has cited a farther Authority for the Antiquity of Gunpowder, and then tells us, The firft Application of this Mixture to Military Affairs feems to have been foon after the Year 1300. Schwartz,

B 4

Schwartz, inftead of being the first Inventor of it, might poffibly be one of the first who thus applied

it. The Account of the Manner in which he came at his Invention very much favours this Opinion. It is faid, that having pounded the Materials of Gunpowder in a Mortar, which he afterwards covered with a Stone, a Spark of Fire accidentally flew into the Mortar, and the Explofion blew the Stone, which covered it, to a confiderable Distance. And perhaps the different Improvements foon added by others, or the Profecution of Bacon's Thoughts in different Places, may have given Rife to the different Dates affigned by Hiftorians for the firft Ufe of Artillery.

The Proportion of the Materials compofing Gunpowder is different from what it was anciently, and the Compofition is thereby render'd by far more efficacious than it originally was. The Invention of Graining it is likewifej a confiderable Advantage. At first it was used in the Form of fine Meal, such as it was reduced to, by grinding the Materials together. And it is doubtful, our Author fays, whether the Graining it was originally intended to increase its Strength, or only to render it more convenient for the filling into fmall Charges, to which alone it was applied for many Years, whilft MealPowder was ftill made ufe of in Cannons. But at laft the additional Strength, which the grain'd Powder was found to acquire from the free Paffage of the Fire between the Grains, occafioned the MealPowder to be entirely laid afide.

The Formation of Artillery, our Author thinks, hath been very little improved in the last two hundred Years; but its Ufe and Application have undergone confiderable Changes; the fame Ends being now generally purfued by fmaller Pieces than what were formerly thought neceffary. Thus the Battering-pieces now univerfally approved of, are the

Demi-Cannons, carrying a Ball of twenty-four Pound Weight; it being found, by Experience, that their Stroke, tho' lefs violent than that of larger Pieces, is yet fufficiently adapted to the Strength of the ufual Profiles of Fortification; and that the Facility of their Carriage and Management, and the Ammunition they fpare, give them great Advantages beyond the whole Cannons formerly employ'd in making Breaches.

But the most important Improvement in the prac tical Management of Artillery, is the Method of firing with small Quantities of Powder, and elevating the Piece fo that the Bullet in its Defcent may go juft clear of the Parapet of the Enemy, and drop into their Works. This Difpofition of Artillery, the Benefit of which Mr. Robins fpecifies, is the Invention of the Marfhal de Vauban, and was firft put in Practice at the Siege of Aeth, in 1692.

Having briefly recited what has been done in the Mechanic Part of Gunnery, Mr. Robins proceeds, in the next Place, to mention the different Theories which have been from Time to Time advanced in relation to the Motion of Shells and Bullets. All thefe he finds to have been founded on falfe Principles; even the later and more learned Writers on: the Art of Gunnery being very much deceived, in fuppofing the Refiftance of the Air to be inconfide-. rable; and thence afferting, that the Track of Shot and Shells of all Kinds is nearly in the Curve of a Parabola By which Means it has happened, that all their Determinations about the Flight of Shot, discharged with confiderable Degrees of Celerity, are extremely erroneous; and confequently it is certain, that the prefent Theory of Gunnery, in this its most important Branch, is ufelefs and fallacious.

Now, to obviate in fome Degree these Imperfections in this Art, our Author has undertaken, in his fecond Chapter, not only to confirm what he has

here

here afferted relating to the Falfity of the Parabolic Motion of these Projectiles, but likewife to afcertain the actual Degree of Refistance which every Shot undergoes according to the Velocity with which it moves; whence," as the Velocity with which "the Bullet iffues from the Piece is eafily known, "by the Principles delivered in his first Chapter,

the Delineation of the Track paffed through by "the Bullet hereby becomes a geometrical Pro"blem; which, indeed, in its utmost Extent, is of " a very complicate and operofe Kind; but in the "Inftances which are most frequent in Practice, "admits of fome very eafy Approximations, which "enable us readily to compare the actual Ranges of Bullets with the Refult of his Theory."

What Mr. Robins has here given us, is but the firft Part of his Defign: He intends another; in which, befides feveral Experiments on the Track defcribed by the Flight of Bullets, and the neceffary. Geometrical Determinations with which they must be compared, he proposes to infert many other Experiments, which, tho' of a miscellaneous Nature, are yet all of them connected in fome Degree with the Theory or Practice of Gunnery. He will also annex to this fecond Part many Maxims and practical Precepts, which will arife from the preceding Principles, and will, he hopes, be of fome Confequence in the future Management of Artillery.

He has divided the Work before us into two Chapters: The firft contains thirteen, the fecond eight Propofitions, with their Demonstrations.

For Inftance, in the firft Chapter, I. He proves, by certain Experiments, that Gunpowder, fired either in a Vacuum or in Air, produces by its Explofion a permanent elaftic Fluid. II. He particularly explains the Circumstances attending the Explosion of Gunpowder, either in a Vacuum or in Air, when fired in the Manger defcribed in the Experiments

now

now mentioned. III. He fhews, that the Elafticity or Preffure of the Fluid, produced by the firing of Gunpowder, is, cæteris paribus, directly as its Den fity. IV. He determines the Elafticity and Quantity of this elaftic Fluid, produced from the Explosion of a given Quantity of Gunpowder. V. He thews how much the Elafticity of the Air is aug-" mented, when heated to the extremeft Heat of red." hot Iron. VI. He determines how much that Elas→→ ticity of the Fluid produced by the firing of Gunpowder, above-affigned, is augmented by the Heat it has at the Time of its Explosion. VII. He folves this Problem: The Dimensions of any Piece of Artillery, the Denfity of its Ball, and the Quan-' tity of its Charge being given, to determine the Velocity which the Ball will acquire from the Explosion, fuppofing the Elafticity of the Powder at the first Instant of its firing to be given. VIII. He determines the Velocity which any Ball moves with, at any Distance from the Piece it is discharged from. IX. He fhews how to compare the actual Velocities, with which Bullets of different Kinds are difcharged from their respective Pieces, with their Velocities computed from the Theory. X. He affigns the Changes in the Force of Powder, which arife from the different States of the Atmosphere. XI." He investigates the Velocity which the Flame of Gunpowder acquires by expanding itself, fuppofing it be fired in a given Piece of Artillery, without either a Bullet or any other Body before it. XII. He afcertains the Manner in which the Flame of Powder impels a Ball, which is laid at a confiderable Distance from the Charge. XIII. He enumerates the various Kinds of Powder, and describes the propereft Methods of examining its Goodness.

Before I proceed to the Titles of the second Chapter, I will here tranfcribe fome Paffages from our Author's Difcourfes on the tenth and thirteenth of

the