involved in the Construction of Artillery. 209 



132. In the physical conditions of application of the impulse as produced 

 by the explosion of powder, however, there are some important differences from 

 any of the cases of application of the strain already assumed, besides that of the 

 total withdrawal of the strain or impulse, almost immediately after its applica- 

 tion, and depending on conditions the precise nature and constants of which 

 are as yet so imperfectly known that it would be useless to pursue tlie appli- 

 cation of analysis to them at present. 



133. Amongst the most important data required is an experimental know- 

 ledge of the rate at which gunpowder inflames in relation to the whole mass, and 

 the curve which shall represent the increase, and subsequent decrease, of pressure 

 on the interior of the gun, from the first instant of ignition, to the moment that 

 the ball leaves the muzzle. (Note L.) Certain formulas are given in gunnery 

 class-books, purporting to represent the time of inflammation of powder, based 

 on the assumption that its grains are spherical and equal, and that the time of 

 burning inwards from the surface to the centre of each sphere, is the same as 

 for the whole mass. The assumption is, however, perfectly fallacious, for 

 obvious reasons. 



But a true result may be arrived at experimentally by a suitable arrangement 

 of galvano-chronometric apparatus with much facility and accuracy; indeed, 

 the author has already (incidentally to his experiments on the rate of transit of 

 earthquake waves in solids, by means of the explosion of small mines) had 

 occasion to determine the time of inflammation for a mass of 25 lbs. of powder 

 (Trans. Brit. Ass., 1851); it would be most desirable that such an inquiry 

 were pursued. Equally so would it be that the curve of pressure within the 

 gun, during the ball's traject through it should be ascertained experimentally. 

 There seems little ground for doubt, that apparatus could be applied to a gun 

 on the principle of the manometer, or rather of the aneroid, or of Bourdon's 

 pressure gauge, such as to receive the pressure as in the interior of the gun, 

 with which it should communicate, and to register it at once in the form of a 

 curve, for every instant of that fraction of a second, occupied by the ball's 

 traject through. 



134. From the extreme rapidity with which the pressure increases within 

 the gun from the moment of ignition up to the point of maximum, a condition of 

 the matter of which it is formed, related to its elasticity, and dependent upon 



