20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Jl 



The whole suspended system was therefore designed to be con- 

 tained in a 3-inch steel pipe, all the essential parts being fastened to 

 a cap, fitting on the top of this pipe. This was done not only for 

 the sake of convenience in handling the heavy chamber, but also from 

 the fact that the o'nly joint that would have to be made air-tight for 

 each shot would be at the 3-inch cap. 



The means of supporting the chamber from the cap is shown in 

 plate 6, figure 2, and plate 7, figure i, the apparatus being shown 

 dismantled in plate 7, figure 2. Two |-inch steel rods, R, R, were 

 threaded tightly by taper (pipe) threads into the cap, C. These rods 

 were joined by a yoke, at their lower ends, which served to keep them 

 always parallel. Two collars, or holders, H and H^ free to slide 

 along the rods R, R, held the chamber or gun, by three screws in 

 each holder. The inner ends of the screws of the lower holder were 

 made conical, and these fitted into conical depressions, c, figure 2(a), 

 drilled in the side of the gun, so that the lower holder could thus be 

 rigidly attached to the gun. This was made necessary in order that 

 lead sleeves, fitting the gun and resting upon the lower holder H', 

 could be used to increase the mass of the suspended system. Three 

 such sleeves were used, the two largest being moulded around thin 

 steel tubes which closely fitted the gun. The rods R, R, were lubri- 

 cated with vaseline. Two -J-inch steel pins were driven through the 

 rods R, R, just above the yoke Y, in order that the latter could not 

 be driven ofif by the fall of the heavy chamber and weights when 

 direct-lift was employed. 



In the experiments in which the chamber and lead sleeves were 

 suspended by a spring, the latter was hooked at its upper end to a 

 screw-eye fixed in the cap C. The lower end of the spring was 

 hooked through a small cylinder of fiber. A record of the displace- 

 ments of the suspended system was made by a stilus, S, plate 6, 

 figure 2, in the upper holder H. This stilus was kept pressed 

 against a long narrow strip of smoked glass, G, by a spring of fine 

 steel wire. This strip of smoked glass was held between two clamps, 

 fastened to a rod, the upper end of which was secured to the cap C, 

 and the lower end to the yoke, Y. Except for the largest charges 

 used, it was possible to measure the displacements on both sides of 

 the zero position, and thereby to calculate the decrement and eliminate 

 friction. 



When the chamber was suspended by a spring, a deflection as large 

 as a centimeter was unavoidably produced merely by placing the 

 cap C on the 3-inch pipe or removing it, although, in all cases the 



