Wheatstone’s instrument was not adopted by our Government, but his idea was followed up and improved upon by Captain Navez, of the Belgian Artillery, who in 1847 brought forward his electro-ballistic pendulum.[485] Only one instrument was now wanting to enable the mechanical effect of the explosion to be directly and completely observed—an instrument to measure the pressure upon the bore of the gun; and this want was supplied in 1861 when Captain T. J. Rodman, Ordnance Department, United States Army, produced his Indenting Apparatus and his Internal Pressure Gauge.[486] The following Table gives the results of some experiments with the new instruments:—

TABLE VI.

Showing the connection between the Size of the Grain, Muzzle Velocity, and Pressure on Bore.

Diameter of
Grains.
Ins.		 Charge.
Lbs.		 Weight of
Shot.
Lbs.		Muzzle
Velocity.
F.s.		Pressure on
Bottom of Bore.
Tons per Sq. In.
.1843126121.5
.15””123521.0
.2””119918.8
.25””115117.1
.3””114615.3
.4””118714.2

This Table shows that as the size of the grain slowly increases, the muzzle velocity decreases very slowly, and the pressure on the bore decreases very quickly. The consequence of this discovery was the manufacture of various very large grained powders such as pebble powder, &c., for heavy guns. But the thorough knowledge of the mechanical effect of the explosion of gunpowder gained by the use of the Navez and Rodman instruments, was of little avail to anybody, for gunpowder had nearly run its course. Just twenty-five years after the introduction of the pressure gauge M. Vieille put the French Government in possession of a nitrocellulose explosive,[487] and gunpowder was added to the list of things that were.

Throughout the whole gunpowder period enthusiasts seem never to have been wanting who believed in the possibility of making smokeless powder and noiseless powder. Castner’s powder, which contained only 3 per cent, sulphur, seems to have been the nearest approach to the former, but no powder containing sulphur could be absolutely smokeless. Whether early gunners suspected this or not I do not know; certain it is, however, that sulphurless powder was under discussion centuries ago. Rabelais (who may have heard soldiers talking about the matter) alludes jokingly to “pouldre de canon curieusement composée, degressée de son soulfre.”[488] In 1756 the French actually experimented with sulphurless mixtures, one of which (80 per cent. sulph. and 20 per cent. ch.) gave good results in range, with very little smoke. It proved to be worthless for military purposes from the difficulty of corning it, and from its crumbling to dust during ordinary transport.[489] The belief in a noiseless powder was scoffed at by Whitehorne: “There be many who bring up lies, saying that they can tell how to make pouder that shooting in gunnes shall make no noise, the which is impossible.” A century afterwards Sir Thomas Browne believed means might be adopted, if not to stifle the sound altogether, at least “to abate the vigour thereof, or silence its bombulation.”[490]

Tables VII. and VIII. give the composition of gunpowder at various times.

TABLE VII.