ON METHODS FOR MEASURING PRESSURES IN THE BORES OF GUNS. 529 



«very 14 inches along it, and his results are given in the annexed table, 

 wliieh is a most instructive one : — 



Examining this table, it will be observed, in the first place, that the 

 muzzle velocities of the equal column projectiles are nearly the same ; 

 that of the 11-inch gun being, as it should be, somewhat the higlier ; 

 hence the energies per square inch must be nearly the same, and the 

 mean pressures per square inch, inducing these energies, must likewise be 

 the same. 



But, for example, comparing the 7-inch and the 11 -inch guns, it will 

 be noted that in the latter gun the pressui'es are always twice and some- 

 times more than four times as great as in the 7-inch gun, the mean 23ressure 

 being nearly three times as great. 



The energy should be in the same proportion ; hence, if the pressure 

 observations had been correct, the observed velocity should have been 

 1,570 f.s., instead of 927 f.s. 



It will be noted also that the forward pressures not only differ greatly 

 in the several calibres, but, for instance, in the 9-inch gun the pressure 

 at 5G inches from the bottom of the bore is double the indicated pressure 

 measured at 42 inches. Rodman accepts the pressures up to and including 

 42 inches as correct, but ascribes the irregular pressures in the chase to 

 the vibrations of the metal due to the discharge. 



Some experiments made by the earlier E.Kplosive Committee fully 

 •explain the cause of the differences between the pressures exhibited by 

 the 7-inch and 11 -inch guns. 



In the first of the experiments of this Committee, they used simul- 

 taneously Rodman's gauge and the chronoscope to which I shall presently 

 ndvert. In the former case of course the pressure was determined 

 latter it was deduced from the motion communicated 

 The results were quite irreconcilable, as a few examples 



directly. In the 

 to the projectile, 

 will show. 



In an 8-inch 



wi 



th 



charge 



of 



lb. of Russian 



prismatic 

 powder and a projectile of 180 lb. weight, fired from a vent a little in 

 advance of the centre of the charge, and called the forward vent, the 

 chronoscope gave a maximum pressure of 20'4 tons, while the Rodman gauge 

 gave maximum pressures in the powder chamber varying from 26*7 to 

 33'7 tons per square inch. In the same gun, under similar conditions, a 

 similar charge of pellet powder gave, with the chronoscope, a maximum 

 pressure of 19-2 tons per square inch, while the chamber pressures given 

 by the Rodman gauge varied from 41 '6 tons to 49*2 tons per square inch. 



But perhaps more striking discrepancies were exhibited by two series 

 of experiments with R.L.G. of Waltham Abbey make, fired from the 

 same gun, and developing in the projectile approximately the same 

 energies. In the first of these series, with a charge of 20 lb. fired from a 

 forward vent, the maximum chronoscope pressure was 13-3 tons, while 



1894. M M 



