

587 



As an instance of this, the hitherto received theory supposes 

 that when a shot is fired from a gun, it acquires its velocity gradually, 

 from the pressure of the elastic fluid generated by the fired powder 

 acting upon it through a certain space. It is also supposed that the 

 initial pressure of this elastic fluid is the same in all cases (the quantities 

 of powder being proportional), whether the gun from which the shot is 

 fired be large or small ; so that the larger the calibre of the gun, the 

 slower the first movement of the shot is supposed to be. The result 

 of the following experiment is given to prove that the first of these 

 propositions is incorrect. The author placed a cast-iron shot 3 inches 

 in diameter and 3 Ibs. 14 ozs. in weight upon a chamber half an inch 

 in diameter and half an inch deep. This chamber was formed in a 

 block of gun-metal, and contained, when filled, one dram of powder. 

 Upon lighting the powder, the ball was driven to a height of 5 feet 6 

 inches ; when the ball was placed at of an inch over the chamber, 

 the charge failed to move it. 



From this it is inferred that the first force of the powder is an impul- 

 sive force, that is to say, it imparts to the shot at once a finite velocity. 

 In order to place the matter beyond a doubt, and to ascertain the 

 relative force of different quantities of powder, the author caused a 

 chamber to be made similar in form to, but of twice the linear dimen- 

 sions of, the former ; he then placed a cast-iron ball of 6 inches 

 in diameter upon the orifice of this chamber, which was filled with 

 powder ; upon firing the latter, the ball was driven up to a height of 

 1 1 feet, that is to say, to double the height of the smaller ; the state of 

 the metal in which the chamber was formed also showed the increase 

 in the initial force of the powder : this is considered to be sufficient 

 proof that the last two of the above-mentioned propositions are as 

 incorrect as the first. 



Assuming the initial force of the powder to be of an impulsive 

 nature, it is not difficult to understand the increase of force shown 

 in the last-named experiment, inasmuch as a certain time being re- 

 quired for the complete conversion of the powder into an elastic fluid, 

 a quantity contained in a chamber of a similar form, but of greater 

 linear dimensions than another, must ignite in a less comparative 

 time, the linear dimensions increasing in the ratio of the first power, 

 arid the quantity of powder increasing in the ratio of the third power, 

 so that the flame will traverse a larger quantity in comparative less time. 



