VOL. XLII.] PHILOSOPHICAL TRANSACTI0K8. 6ff 



closed and contracted, and the worm may be discovered through the skin, as it 

 lies coiled in his stomach. In these last 5 figures it may be noted, that, how- 

 ever extended and swelled the stomach of the insect appears, the posterior part 

 is not stretched in proportion, but discovers itself every where as a small tail, in 

 which is contained a gut, with which the stomach communicates. Fig. 12 

 shows one of the horns or arms of a polypus very much magnified, for giving 

 some imperfect idea of the knots or papillas in the transparent membranous 

 substance, of which it is composed. Fig. 13 represents a polypus that had 

 several young growing from it at once, some of which had also others springing 

 out from them again. Besides those here represented, 8 other young ones 

 had at several times separated themselves from him, since the insects were 

 received. 



yin Account * of a Book intitled, New Principles of Gunnery, containing the 

 Determination of the Force of Gunpowder ; and an Investigation of the re- 

 sisting Power of the Air to swift and slow Motions. By B, R. F. R. S. as far 

 as the same relates to the Force of Gunpowder. N° 469, p. 437. 



This treatise contains 1 chapters. The first treats of the force of gunpowder, 

 and the velocities communicated to bullets by its explosion : the 2d considers 

 the resistance of the air to bullets and shells moving with great velocities ; and 

 endeavours to evince, that this resistance is much beyond what it is generally 

 esteemed to be ; and consequently that the track described by the flight of these 

 projectiles, is very different from what is usually supposed by the modern writers 

 on this subject. 



The principal points endeavoured to be established in the first chapter are 

 these, " That the force of fired gunpowder is no more than the action of a 

 permanent elastic fluid, which is produced by the explosion; that this fluid ob- 

 serves the same laws with common air in their exertion of its pressure or elasti- 

 city ;" and consequently, " That the velocities communicated to bullets by the 

 explosion may be easily computed from the common rules, which are established 

 for the determination of the air's elasticity." 



The first 2 propositions contain the proofs that a permanent elastic fluid is 

 constantly generated in the explosion of gunpowder. The 3d proposition is, 

 that the elasticity of this fluid produced by the firing of gunpowder, is, caeteris 

 paribus, directly as its density. This is proved both by the author's own ex- 

 periments, and by several of Mr. Hauksbee's ; when, by the firing of 26 quan- 

 tities of powder successively, the mercurial gauge was sunk from 294^ inches, to 



* This account was given by the very ingenious author himself, Mr. Benjamin Robins. 



