216 Capt. Sir A. Noble. [June 21, 



of comparing the velocities and energies developed by the new explo- 

 sives is by the aid of diagrams. 



Accordingly, in Fig. 1, I show the velocities of seven different 

 explosives from the commencement of motion to the muzzle of the 

 gun ; the position of the points at which the velocity is determined 

 are shown, and on the lowest and highest curves the observed 

 velocities are marked where it is possible to do so without confusing 

 the diagram. Lines are drawn to indicate the velocities that are 

 obtained with the lengths of 40, 50, 75, and 100 calibres. 



Fig. 2 shows the pressures by which the velocities of Fig. 1 

 were obtained. The areas of these curves represent the energies 

 realised, and the lines intersecting the curves indicate the pressures 

 at which the gases are discharged from the muzzle for lengths of 

 40, 50, 75, and 100 calibres respectively. The chamber pressures 

 indicated by crusher gauges are also shown in Fig. 2, and it will 

 be observed that the two modes of determining the maximum pres- 

 sure are in general in close accordance. 



It will further be observed that with the slow-burning powders 

 the chronoscopic maximum pressures are somewhat, though not 

 greatly higher, than are those indicated by the crusher gauges. 

 This observation is not new.* It was noted in the long series of 

 experiments with black powders carried on by the Committee of 

 Explosives. 



The result is widely different where an explosive powder or a 

 quickly-burning powder, such as R.L.Gr., giving rise to wave-pressure 

 is employed ; the crusher gauge in such casesf gives considerably 

 and frequently very greatly higher pressures, and this peculiarity is 

 illustrated in the curve from .B.L.G. in Fig. 2. 



It is, perhaps, hardly necessary to point out that the results given 

 in Fig. 1 have to be considered in relation to the facts disclosed in 

 Fig. 2. Thus it will be noted that the velocities and energies 

 realised by 22 Ib. of 0'35-in. cordite and 20 Ib. of 0'3-in. cordite are 

 practically the same, but reference to Fig. 2 shows that with the 

 0'3-in. cordite this velocity and energy has been obtained at the cost 

 of nearly 30 per cent, higher maximum pressure. 



A similar remark may be made in regard to the French B.N. 

 powder if compared with the ballistite. Its velocity and energy are 

 obtained at a high cost of maximum pressure, and it is interesting 

 to note how the velocity curve of B.N\, which for the first four 

 feet of motion shows a velocity higher than that of any other ex- 

 plosive, successively crosses other curves, and gives at the muzzle a 

 velocity of 500 f.s. under that of cordite. 



The velocities and energies at the principal points indicated in 



* Noble and Abel, ' Phil. Trans.,' TO!. 165, p. 110. 

 t Compare Noble and Abel, loc. tit., p. 109. 



