61 
Tlie fact that if two complete charges were put into the 
gun, the powder of the second charge would he directly 
beneath the point of rupture appeared in favour of this, the 
easiest mistake. But would, supposing the powder to have 
been pebble powder, the pressure from the two charges have 
been sufficient to cause the result ? At first it seemed to me 
that even supposing that the second charge had been ignited 
by the first, which was doubtful, this would not explain the 
suddenness or magnitude of the pressure. But on further 
consideration it appeared certain that the second charge 
would not be ignited by the fire from the first ; and it then 
became clear that in this very fact we should have an amply 
sufficient explanation of the excessive pressure. 
My object in writing this paper is to point out the proba- 
bility of this explanation, and so, if possible, to induce the 
authorities to test it. It occurred to me several days before 
the report of the Committee appeared, and in spite of the 
improbability of such a mistake as double loading, I could 
not shake off the conviction that it afforded the true expla- 
nation. As I have pointed out, the blowing into fragments 
of a wrought-iron tube implied an explosive action such as 
might result from gun cotton or dynamite but which could 
not be produced by the slow burning of pebble powder. 
The point to be explained then is how the second charge 
could be brought into such a condition that it would explode 
like gun cotton. To understand this it must be remem- 
bered that in the usual way the grains of gunpowder burn 
from their outside only, so that the thicker the grains the 
longer will be the time occupied in burning, and for the 
same weight of powder the slower will the gas be given off. 
The reason why gun cotton is so much more destructive than 
gunpowder is not that it gives off more gas weight for 
weight, but that when ignited by a flash it burns so much 
quicker. If, therefore, by any means the whole mass of gun- 
powder could be heated up to the firing point at the same 
