VOL. LXXI.] 



PHILOSOPHICAL TRANSACTIONS. 



101 



but Mr. Robins endeavours to account for that circumstance on different prin- 

 ciples, and supports his opinion by showing that every increase of the charge 

 within the limits of practice produces a proportional increase of the velocity of 

 the bullet, and that when the powder is confined by a great additional weight, 

 by firing 2 or more bullets at a time instead of 1, the velocity is not sensibly 

 greater than it ought to be according to his theory. 



If this were a question merely speculative, it might not be worth while to 

 spend much time in the discussion of it ; but as it is a matter upon the know- 

 ledge of which depends the determination of many important points respecting 

 artillery, and from which many useful improvements may be derived, too much 

 pains cannot be taken to come at the truth. Till the manner in which powder 

 takes fire, and the velocity with which the inflammation is propagated, are 

 known, nothing can with certainty be determined with respect to the best form 

 for the chambers of pieces of ordnance, or the most advantageous situation for 

 the vent ; nor can the force of powder, or the strength that is required in dif- 

 ferent parts of the gun, be ascertained with any degree of precision. 



As it would be easy to determine the best situation for the vent from the 

 velocity of the inflammation of powder being known, so on the other hand I 

 had hopes of being able to come at that velocity by determining the effect of 

 placing the vent in different parts of the charge ; for which purpose the follow- 

 ing experiments were made. 



By the annexed experiments 

 it appears, 1st, that the differ- 

 ence in the force of any given 

 charge of powder which arises 

 from the particular situation of 

 the vent is extremely small. 



2dly. From the result of all 

 these experiments it appears, that 

 the effect of placing the vent in 

 different positions with respect to 

 the bottom of the chamber is dif- 

 ferent, in different charges; thus, 

 with \6d grains of powder, the 

 velocity of the bullet was rather 

 diminished by removing the vent 

 from 0, or the bottom of the 

 bore, to 1.32; but with 218 

 grains of powder the velocity was 

 a little increased, as was also the 

 recoil. With 290 grains of pow- 

 der the velocity was greatest 



Experiments showing the effect of placing the vent in differ- 

 ent parts of the charge. 



