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23.

lower end to the yoke, [[underlined]] Y [[/underlined]]. 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 [[underlined]] C [[/underlined]] on the 3-inch pipe or removing it, although, in all cases the system would return to within one millimeter (usually much less than this) of the zero position after being displaced. In order to avoid any such displacement as that just mentioned, an eccentric clamp, [[underlined]] K [[/underlined]], Fig. 15, was employed to keep the suspended system rigidly in its zero position during assembling and dismounting the apparatus.

This clamp consisted of an eccentric rod, [[underlined]] K [[/underlined]], free to turn in a hole in the cap [[underlined]] C [[/underlined]], the lower end being held in a bearing in the yoke [[underlined]] Y [[/underlined]]. Through the upper end of this rod was pinned a small rod [[underlined]] K' [[/underlined]], at right angles to [[underlined]] K [[/underlined]]. The surface of the rod [[underlined]] K [[/underlined]] was smeared with a mixture of bee's wax, resin, and Venice turpentine; and the hole in the cap through which [[underlined]] K [[/underlined]] projected was rendered air tight by wax of the same composition.

The suspended system was assembled while the cap [[underlined]] C [[/underlined]] was held by a support touching its under side. When the assembling was complete, the wax was heated by a small alcohol blow torch until it was soft, then a rubber band was slipped around the rod [[underlined]] K' [[/underlined]] and the outlet pipe E. A trial showed that the cap could now be put in place on the pipe and removed, without the suspended system moving appreciably. After the cap [[underlined]] C [[/underlined]] was in position on the pipe, the rubber band was removed, and the wax heated until the rod [[underlined]] K [[/underlined]], could be turned out of engagement with the holders [[underlined]] H [[/underlined]], [[underlined]] H' [[/underlined]]. After a shot had been