. Carnegie Institution of Washington publication. 118 DISPLACEMENT INTERFEROMETRY APPLIED TO Thus, after integration of the equated values of dW, Rr p' A0 = —rr- log — JK p The constant factor is about 83 , since Naperian logarithms are needed. In this way the values above given were obtained. They represent the total accumulation of heat in over half an hour; but it is at once radiated by the gas and finds lodgment on the walls of the apparatus. Even if these radiated nothing, their temperature increment would be infinitesimal in the ratio principally of their mass to the mass of the air-
. Carnegie Institution of Washington publication. 118 DISPLACEMENT INTERFEROMETRY APPLIED TO Thus, after integration of the equated values of dW, Rr p' A0 = —rr- log — JK p The constant factor is about 83 , since Naperian logarithms are needed. In this way the values above given were obtained. They represent the total accumulation of heat in over half an hour; but it is at once radiated by the gas and finds lodgment on the walls of the apparatus. Even if these radiated nothing, their temperature increment would be infinitesimal in the ratio principally of their mass to the mass of the air-content (probably for the plenum gram to several kilograms), which is then further diminished by radiation. The available heat does not differ as much at all the pressures as does the temperature. I question whether such small thermal effects, if they are such and so circumstanced, could be detected in any other way. 93. Experiments with the exhausted case.—The case, figure 139, having been carefully sealed, measurements were made in partial vacua, as shown in figure 150, for an exhaustion between 20 and 30 cm. and figure 151, for an I«I;\K:. exhaustion between 37 to 45 cm. In the former an error was made in the second triplet, which is therefore discarded. It is seen at once that, as the ex- haustion increases, the drift grows less and the triplets are nearly repetitions of each other. The double amplitude changes but little; thus, for Plenum, £ = 76 cm. Vacuum, 51 cm. Vacuum, 35 cm. a result to be anticipated, if the viscosity of air is independent of pressure, and in view of the very slow motion of the needle, the resistance is not due to tur- bulent motion of the air. The case leaked slightly, but this does not seem to be of moment here. An important consequence follows : Since the frictional resistance is inde- pendent of pressure, it may be computed as a case of viscosity, the problem being that of a cylindrical shaft rotating on a normal axis, at it
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