Plane Reflection of Sound, as Exhibited by the Pinhole Resonator.

if but a single square cm. on each glass face radiates toward m. As there are a number of such square cms., contributing radiation, the coefficient of (3) would be decreased ten or twenty times. One may conclude I think that AO compared with AYr is numerically much in excess. This implies too large a AO, to persist in a room of practically constant temperature, in the summer. It is thus more than probable that at a vacuum of 10-8 mm. or a force of .22 dynes on each shot, so small a part as 10 or 20 times the 10-8 X 70 X Ay, instanced in equation (1) may remain fluctuating .in value with small changes in the radiating thermal environment. Measurement of 'y in Terms of the Viscosity ofAir.-A maximum deflection of the m-balls is produced by placing the M-balls in position. When this is attained, the latter are reversed and the velocity v with which -the needle (filamentary frame) passes through the equilibrium position, is measured with a stopwatch. The M-balls are then again reversed and the measurement of v repeated; etc. In a plenum, the motion of the needle through the zero point is practically uniform and therefore the frictional force is equal to the gravitational pull. Moreover, if two points of the scale near to and equidistant from the zero point are selected for releasing and arresting the stopwatch, the torsion of the fibreacts to the same degree as an acceleration and a retardation. The frictional resistance encountered by either round mass m of radius r is by Stokes' equation 6wrirv, Where ? is the viscosity of air. The velocity v of the balls m is v = (1/2L) Ay/At