230 ^^''- F, J. BramireU [June 13, 



pound had devoted to it 60 cubic inches of space, the intensity of the 

 explosion would be greatly reduced. While on the other hand, if the 

 powder were made into a solid block occupying the space demanded 

 by its specific gravity of 1-76, namely only 16 cubic inches, and if 

 that block could by some means, say by threading it in all directions 

 with platinum wires, be made red hot by electricity, and be ignited 

 throughout simultaneously, the intensity of the explosion would be at 

 a maximum. 



There is no need for me to tell you that it is in the highest 

 de<-^ree important in designing a gun, that the designer should know 

 with a considerable approach to accuracy, what are the pressures the 

 gun may be called upon to sustain, and what are the varying pres- 

 sures to be expected in the different parts of the same gun. Now 

 there are two modes by which the pressures may be ascertained. 

 The first mode is by calculation from the velocity of the projectile 

 or from the recoil of the gun, if it could be left free to recoil ; the 

 second mode is by the introduction of pressure gauges called from 

 the mode in which they are acted upon " crusher " gauges placed 

 within the gun itself. I have already shown you how if the 

 velocity of the shot when it leaves the muzzle is known, and the 

 weight of that shot, and of the powder which is also in motion is 

 known, and the distance from the part of the bore where the base 

 of the shot was situated before it started to the muzzle is known, 

 it is comparatively easy to calculate, after making due allowance for 

 the pressures required to set up rotation, the mean pressure that has 

 been exerted in the gun, but (as I have stated) the information thus 

 arrived at does not tell the inquirer what the varying pressures 

 have been, nor what the maximum pressure has been. But if it 

 were possible to ascertain what was the velocity of the projectile, 

 say when it had traversed half-way along the bore, it would then be 

 easy to compute the average pressure which had prevailed from the 

 commencement of the journey to this half-way point, and then the 

 average pressure from this point to the muzzle ; and this clearly would 

 be a step gained in the solution of the question, what are the varia- 

 tions of pressure during the passage of the shot ? Similarly, if the 

 length of the traverse of the shot in the gun were divided into 

 say ten parts, and the velocity as the shot passed each of these 

 imaginary points of division could be known, the average pressure 

 in each section could be calculated, and thus the maximum pressure 

 and the variations would be ascertained. You will, I think, agree 

 with me that it is a difficult task to detect at what speed a projectile 

 is travelling when ten or twelve feet within the bore of a gun. The 

 way in which up to a certain date this information was obtained with 

 small arms, was to cut off successive lengths from the barrel of a rifle 

 so that each part of the barrel in turn became the muzzle, and thus 

 the velocity of the bullet as it issued could be recorded in the usual 

 manner. But this mode would be a costly one to pursue with large 

 cannon, and, moreover, it is open to the great objection that a record 



