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34.

there is a considerable space between the gun and the 3-inch pipe, through which the gas may pass and, accumulating above, exert a [[underlined]] downward [[/underlined]] pressure on the top of the gun.

One important advantage of the spring impulse-meter over that employing direct lift is that the former has very little friction, so that the readings are very reliable. Another advantage is that the displacement of the former will include without any uncertainty the effect of any number of rebounds following one another in rapid succession; i.e., the effect of multiple reflections of the gas, if such reflections are present.

[[underlined]] EXPLANATION OF TABLE III [[/underlined]].

In the vacuum experiments, the soft-steel chamber was used for Du Pont powder, and the nickel-steel chamber for Infallible powder.

The three nozzles called short, medium, and long, were respectively, 9.64, 15.88, and 22.08 cm. from the throat to the muzzle.

The length of chamber, [[underlined]] l [[/underlined]], in the third column, is taken as the distance shown in Fig. 6(a).

In the cases of simple harmonic motion in which [[underlined]] d  [[/underlined]] [[subscript]] 2 [[/subscript]] is not given in the table, the displacements were so large that [[underlined]] d [[/underlined]][[subscript]] 2 [[/subscript]] was prevented from reaching its full extent by the yoke, [[underlined]] Y [[/underlined]], Fig. 15. Correction for friction was made in these cases by choosing the decrement from some other experiment that would be likely to apply. The number of this experiment is written in parenthesis, in the Table, in place of [[underlined]] d [[/underlined]] [[subscript]] 2 [[/subscript]]. The same procedure is followed in the experiments with direct lift.