MECHANICS AND USEFUL AKT3. 61 



gun. it acquires its velocity gradual!}", from the pressure cf the clastic fluid 

 generated by the fired powder acting upon it through a certain space. It is 

 also supposed that the initial pressure of the 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, three 

 inches in diameter, and three pounds fourteen ounces 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 

 five feet six inches. When the ball was placed one-eighth 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 impulsive 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 dimensions of the former; he then placed a cast-iron ball, of six 

 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 eleven 

 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 of 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 required 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, and the quantity of powder increasing in the 

 ratio of the third power, so that the flame will traverse a larger quantity in 

 comparatively less time. Thus it appears that the powder which inflames 

 more rapidly has a much greater initial force, being more concentrated in 

 its action; a quick burning powder, therefore, is better for ordnance of 

 small length, such as mortars and iron howitzers. The different results pro- 

 duced by powder of different quality have, according to the author, been 

 entirely overlooked in the hitherto received theory. This theory, which 

 considers the secondary force, namely, the elasticity of the fluid only, and 

 takes no account whatever of the enormous impulsive or initial force pro- 

 duced by the sudden conversion of the powder into an clastic fluid, is that 

 which regulates the system upon which ordnance are at present constructed; 

 hence the reason why large guns are so liable to burst so much so, that it 

 has been said that no gun larger than a thirty-two pounder is safe to fire. 



From the variety of experiments made by the author, he arrives at the 

 conclusion that when powder is of the same quality, and confined in cham- 

 bers of similar form but, of different sizes, the initial force varies, within cer- 



U' 4 - 



tain limits, in the ratio of - J , where iv \& the weight of the powder, and w' 



of the ball. Thus, were this new theory recognized, the question of the 

 increase of .strength, with increased thickness of metal, would wear an 



