300 THE SCIENTIFIC PAPERS OF 



guns for the Prussian Government. The weight of his 12-pounder 

 breech-loading gun was 825 Ibs. The cost of the forging was 

 about 93, and that of the gun complete was 150. These figures 

 would enable a comparison to be made with the cost of guns of 

 other constructions. With regard to composite guns, he would 

 suggest, that although they might possess greater strength against 

 internal pressure, than a gun of homogeneous metal, yet such a 

 gun would be more liable to injury, when hit by a hostile shot. A 

 composite gun would, he thought, suffer more from that cause, than 

 a gun of homogeneous metal, which would only be indented by a 

 shot ; whereas the composite gun would probably be disabled. 



Hitherto comparatively few experiments had been made, to 

 determine what the pressure upon the interior of a gun really 

 was in firing, and also what was the resistance of the atmosphere 

 to shot at different velocities. In 1846 his brother, Mr. Werner 

 Siemens, suggested a plan to a Commission appointed by the Prus- 

 sian Government, the results of which had been published. He 

 determined the velocity of the shot by making it pass insulated 

 wires, in connection with a Ley den jar. The electrical discharge 

 passing through the shot, caused a spark to go from a point upon 

 the polished surface of a steel cylinder revolving at high velocity, 

 causing it to be marked by a speck of burnt metal. The shot in 

 striking other wires, at a given distance, would make another 

 speck upon the polished steel cylinder, and the angular distance 

 between those two points would represent the time that was 

 occupied by the ball in passing from the one place to the other. 

 The results that had been obtained by this apparatus, were, how- 

 ever, not quite satisfactory ; and it had occurred to Mr. C. W. 

 Siemens, that in order accurately to ascertain the forces acting in 

 a gun, and also the resistance of the atmosphere to the passage of 

 the projectile, an apparatus of a more simple nature might be con- 

 structed, which should record those facts, in the same way that the 

 exact pressure of steam in a steam cylinder, at every portion of 

 the stroke, was arrived at. His object was, in fact, to indicate the 

 forces acting upon the projectile throughout its flight. For this 

 purpose he proposed to employ a hollow shot with open ends, 

 closed by strong doubly-dished steel plates, laid one upon another, 

 with lead plates between. When the shot was fired, the gases of 

 the powder would act upon the end diaphragm, the pressure upon 



