THE EOYAL ARTILLERY INSTITUTION. 
431 
and which, acting on the “ crusher 99 and walls of the gun would, in the 
first instance, produce effects on each varying with their masses, the spaces 
described, and the resistances, and afterwards set up an action which would 
be most felt by the “ crushers,” because they would partake both of their 
own motion and that of the walls of the gun. 
There is yet another supposition which would account for these pressures. 
If the charge when ignited burn uniformly, the grains nearest the point 
of ignition will naturally be in a more advanced state of combustion than 
those further away. 
A great pressure and temperature will arise, causing increased combustion, 
which will be most felt where the greatest amount of powder remains to be 
consumed, and where it may be supposed to be a mass of half-burnt grains 
crushed to dust by the pressure proceeding from the point of ignition—a 
condition most favourable for intensely rapid combustion. Thus sudden 
local pressures would be manifested at these points and be continued through 
the chamber by a sort of wave motion, which, passing backwards and for¬ 
wards, would manifest the greatest effects where the direction of its motion 
was changed, viz., at the base of the shot and at the bottom of the bore. 
The facts that indentations are found in the bore at the base of the shot, 
and also that so much trouble has been found in preserving the bottom of 
the bores from the action of the powder, appear to favour this view. The 
continued action throughout the bore also accords with it. On this sup¬ 
position the pressure would be often repeated, but the whole of the chamber 
would not be under its influence at the same time, and the structure of the 
gun would not be so injuriously affected as the more limited surfaces of the 
crushers. 
These anomalous pressures would thus appear to be due to one or other 
of two causes—either a wave motion in the gas originated somewhat in the 
manner described, or a vibration or wave motion in the walls of the gun, set 
up either by a very intense water pressure, or by a less intense gaseous 
pressure suddenly applied. 
I have long been favourable to the notion that the wave motion exists in 
the gas; but a consideration of the enormous pressure of which gunpowder 
is capable, and the exceeding rapidity with which it is augmented, make me 
doubtful if the action be not due to vibration in the walls of the gun, and 
of a very dangerous character. The practical point is to decide between 
these two view's, and to determine whether the destructive action in the gun 
is comparable to the indications of the crushers. 
The.se questions, though very necessary, are of such extreme delicacy that 
the chronoscope must fail to detect them, owing to the fact that it does not 
note the motion of the projectile continuously throughout the bore, but only 
from point to point; so that a pressure of great intensity but very short 
duration, may occur between two points of observation which cannot be 
separated from the general law of pressure, but .must be absorbed in it, 
causing a modification. 
The action in question we may assume to be originated during the initial 
stages of the shot’s motion, w r here the wires of the chronoscope are 2 ins. 
apart. The maximum pressure is attained even with the slowest burning 
powder before the third wire is cut, so that only two spaces of time are 
measured at this important point. If we take into consideration that the 
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