226 ^Ir. F. J. Bramwell [June 13, 



certain temperature is reached, and as that temperature when a light 

 is applied to powder proceeds from the outside towards the centre of 

 each grain, it is, as I have said, easy to see why, if a pound of powder 

 be made into a single grain of about 3^ inches cube, and heat be 

 applied to the outside of such a grain so as to cause ignition to take 

 place, more time will be required for the combustion of such a pound 

 of pow^der, owing to the slowness with which the heat would travel 

 from the outside to the centre of a grain of these dimensions as 

 the powder burnt away, than would be required if the pound of powder 

 were made into 16 grains of 1 inch cube each, and these were simul- 

 taneously heated on their exteriors to the temperature of ignition. 

 And following this up, one understands readily how much more rapid 

 would be the burning of the powder if the same weight, instead of 

 being in the form of 16 cubes of an inch each, were in the state of 

 thousands of small grains. In short, one can readily see why it is 

 that the larger the particles, the slower the combustion. 



I need hardly say that the expressions quick and slow are but 

 comparative terms, and that even the slowest of gunpowders finishes 

 its combustion in what is popularly called " no time." But " no time " 

 though it be, the unassisted eye can readily detect the difference in 

 the rate of burning due to variations in the size of the powder. 



I will now ask Professor Abel, who, I am glad to say, is with us 

 to-night, to show you by an experiment which he has kindly prepared, 

 that there is this marked difference in the rate of combustion in powder 

 of varying sizes. 



I will next endeavour to explain in what way it is that the slower 

 combustion, while equally ef&cacious in propelling the shot, acts less 

 severely on the gun. 



We will take it, that the object to be obtained by the explosion of 

 powder behind a projectile in a cannon, is to cause that jn-ojectile to 

 issue from the muzzle with a certain velocity. About a quarter of a 

 mile, that is, 1320 feet in a second, is now-a-days a low velocity. 

 I have already, when speaking of the rifling, suggested, by way of 

 illustration a speed of 1400 feet a second; but, although it does 

 not immediately concern this lecture, it may be of interest to remark, 

 that by special arrangements as much as 2265 feet per second have 

 with a projectile of 160 lbs. been obtained. In the present instance, 

 to illustrate that which I wish to convey to you, I will again assume 

 a speed of 1400 feet. Such a velocity would be produced in a 

 fulling body by a descent (through a vacuous space, so as to be 

 unresisted by air) of about 30,000 feet, or 5j miles, and the stored- 

 up energy in a projectile moving at 1400 feet would be equal to its 

 weight multiplied into the height through which it must fall to 

 attain the velocity, that is to say, in the case of the 1400 feet sup- 

 posed, if the projectile weighed 6 cwt. or i of a ton, then 30,000 feet 

 multiplied by a ^ would give 7500 foot tons as the stored-up energy. 

 Now, if this velocity were got by the action of gravity, and if one be 

 allowed to leave out of consideration atmospheric resistance and the 



