CAPTAIN NOBLE AND ME. E. A. ABEL ON EIRED GUNPOWDER. 
55 
after the cylinder has travelled 8 inches it will be withdrawn from the action of the 
charge. If, then, we know the velocity of the cylinder, we know that of the projectile 
■when it has travelled 8 inches. Again, if we make the section of the cylinder half that 
of the projectile, it will describe in the same time double the space and have acquired 
double the velocity, and so on ; so that, for example, if the section of the cylinder be 
one eighth of that of the projectile, we shall, if we know the cylinder’s velocity, know 
that of the projectile when it has travelled 1 inch. 
The general results at which the Prussian Committee arrived were, that in the 
6-pounders the maximum pressure realized was about 1100 atmospheres (7’2 tons per 
square inch), and in the 12-pounders about 1300 atmospheres ( 8’5 tons per square inch). 
They further found that, with every charge with which they experimented, two maxima 
of tension were distinctly perceptible. 
These experiments were made the subject of an elaborate memoir by the distinguished 
Russian Artillerist General Mayevski*, who confirmed generally the results arrived at 
by the Prussian Committee. 
Between the years 1857 and 1859 Major Rodman made an extensive series of 
experiments on gunpowder for the United States Government. 
The chief objects of Rodman’s experiments were: — 1st, to ascertain the pressure 
exerted on the bores of their then Service Guns ; 2nd, to determine the pressures in 
guns of different calibres, the charges and projectiles in each calibre being so arranged 
that an equal column or weight of powder was behind an equal column or weight of 
shot ; 3rd, to investigate the effect produced on the gaseous tension in the bore of a 
gun by an increment in the size of the grains of the powder ; and 4th, to determine 
the ratio which the tension of fired gunpowder bore to its density. 
In carrying out these experiments, Rodman made use of an instrument devised by 
himself, and since extensively used on the Continent. It is represented in Plate 14. 
fig. 1, and consists of a cylinder, A, communicating by a passage, B, with the bore 
of the gun or interior of the vessel, the pressure existing in which it is desired to 
measure. 
In the cylinder is fitted the indicating-apparatus, consisting of a piece of copper, C, 
against which is placed the knife D, shown in elevation and section. The pressure 
of the gas acting on the base of the piston E causes the indenting-tool to make a cut 
on the soft copper, and, by mechanical means, the pressure necessary to make a similar 
cut in the copper can be determined. 
A small cup at F prevents any gas passing the indenting-tool, while the little channel 
G allows escape should any, by chance, pass. 
Rodman considered that his experiments showed that the velocities obtained in large 
guns with the service small-grained powder might be obtained, with a greatly diminished 
* Revue de Technologie Militaire, tom. ii. p. 174. 
t Experiments on Metal for Cannon and qualities of Cannon Powder. Boston, 1861. 
