1879.] on the ' Thunderer ' Gun Explosion. 229 



lino A B represents tlic length of the bore traversed by tlie shot, and 

 that the vertical lines represent tons pressure per square inch ; and 

 assume that the black vertical dotted line A to D represents 24 tons 

 and is tlie maximum pressure arising from burning the charge of 

 jiebblc powder, and that this pressure is maintained for a very short 

 time, and therefore through a very small distance as represented by 

 the summit C of the hillock to which I now point, and that then by 

 the increase of space arising from the moving of the shot and by the 

 cooling of the gases the pressure diminishes until when the shot is 

 leaving the muzzle of the gun, the pressure has fallen to 2^ tons on 

 the square inch, as represented by the height B E. The average of 

 these varying pressures will be represented by the dotted line x y, 

 and will be found to be about 5 tons per square inch ; which pressure 

 when applied on the area of the base of a 12-inch projectile, equals 

 568 tons, or 2069 times the weight (as I shall jjresently have occasion 

 to tell you) of the common shell, empty, but with its gas check, for 

 this gun. The maximum strain you will see to attain this average 

 pressure has been only 24 tons to the square inch. 



Assume next that a quick-burning powder had been used, and that 

 this had given a maximum pressure, as shown by the dotted line 

 A F, of 30 tons on the inch, but that this i^ressure had continued for 

 a still shorter time and for a less distance, as shown by the position of 

 the hillock G, and had then fallen until at the muzzle it retained 

 only the pressure expressed by B N. The average would still be 

 represented by the line x y, and the effect in propelling the shot 

 would be just the same as before, but the gun would have been 

 strained by a maximum pressure of 30 tons per inch, instead of by a 

 maximum pressure of only 24 tons. 



Although Diagram 6 represents the varying pressures which 

 propel the projectile, it does not, until after the maximum pressure 

 is reached, that is to say it does not, except in front of the point of 

 maximum pressure, represent the extent to which the gun is subjected 

 to these pressures. In the absence of wave action (to which action I 

 shall have to refer hereafter), if a pressure exists at the base of the 

 shot, that same pressure must prevail throughout the bore of the gun 

 to the rear of the shot. Diagram 6a correctly shows the strains which 

 come upon the gun under the conditions of propelling pressure repre- 

 sented in Diagram 6. 



From that which I have just been saying, you will be i^repared 

 to hear that, other things being equal, the intensity of the explosion 

 is increased when the space occupied by the powder is diminished. 

 In practice the cartridges are made of such length, that every pound of 

 powder as it lies in the gun between the base of the projectile and the 

 rear end of the bore, reposes in a space the cubic contents of which are 

 30 inches, or rather more than the contents (27J inches) of a pound of 

 water, and if the cartridge were made of double the length and of cor- 

 respondingly attenuated girth, so that the powder lay with practical 

 uniformity in the cartridge along the bottom of the bore, and thus each 



