1880.] Sequel to the ' Thunderer ' Gan Explosion. 325 



pressure would be much reduccc!. Let us iinagiuo the cartridge to 

 be made up of a number of parallel cylinders of powder, each cylinder 

 being 1 inch in diameter, and of the whole length of the cartridge, 

 and assume that the projectile is, in length, say 2.^ times the diameter 

 of the bore of the gun. Then, in a G-inch gun, the i)rojectilo would 

 be 15 inches long, and each of the imaginary cylinders of powder of 

 1 inch diameter would find the exi)ansion of the gases arising from its 

 combustion opposed by the inertia of a cylinder of iron 1 inch 

 diameter by 15 inches long. But if the gun were 12 inches diameter 

 of bore and the shot 2^ diameters in length, then each cylinder of 

 powder of 1 inch diameter would find the expansion of the gases 

 arising from its combustion opposed by the inertia of a cylinder of 

 iron of 30 inches long. This circumstance should be borne in mind 

 when considering the results arising from cases of double-loading 

 which have from time to time occurred in comparatively small 

 cannon. 



Fui'ther, as pointed out by Mr. Osborne Reynolds, now nearly a 

 year ago, it is not impossible that the front charge may have been 

 ignited by the rise in temperature caused by the conversion of a 

 portion of the energy in the rear projectile, into heat. It is by no 

 means difficult to ignite gunpowder in this way. 



The bursting charge of a Palliser shell, for instance, consists of 

 powder without any fuse or detonating composition to ignite it ; but 

 by the striking against an armour plate the velocity of the shell is so 

 materially reduced, that the powder contained within it continuing 

 to rush forward, strikes the front end of the shell, and by this mere 

 stoppage generates sufficient heat to ignite itself. 



I have here an apparatus similar to one used by Professor Abel 

 many years ago to investigate this question. Professor Abel, I am 

 glad to say, is present with us and will exhibit it to you. It consists 

 simjDly of a falling weight, the effect of which is received upon a small 

 brass plate lying upon a thickness of one-twentieth of an inch of 

 powder, having an area of about one-fifth of a square inch; the 

 weight is 50 lbs., and by falling from a height of 12 feet it explodes 

 the powder. 



I may mention that a gunpowder pile-driving engine has been 

 used. I have not seen it in operation, but according to what I have 

 read of it, a charge of powder being placed in a cavity in an iron cap 

 on the jiile and being struck by the falling monkey, is thereby ex- 

 ploded, driving the pile downwards and the monkey upwards ; and 

 then a fresh charge being inserted before the monkey has time to 

 descend, is in its turn exploded ; and in this way the pile is driven. 



As you see, explosion can be obtained by the mere effect of a small 

 falling weight, and it does not seem improbable, looking at the im- 

 mense energy in the rear of the front charge of powder, that enough 

 heat may be generated to raise that powder to the point of combus- 

 tion, either just in the rear of the cartridge, causing a local raising of 

 the temperature and the ignition of the powder at this part, or what 



