The paper describes the measurement of the influence of pressure on the viscosity of five commercially pure gases: air, nitrogen, hydrogen, argon, and helium, in a range up to about 70 atm (1000 psi) at room temperature (20 or 21 C). The viscosity was measured by observing the period of oscillation and the logarithmic decrement of an optically ground quartz disk of 70 mm diam suspended on a thin rhodium-platinum wire between two fixed optically ground quartz plates with a separation of 1 mm and performing torsional oscillations. The data were evaluated on the basis of Macwood’s equations, but the instrument proved capable of a higher accuracy of measurement than the 1 per cent inherent in the theory. The scatter of experimental data did not exceed 0.1 per cent and repeatability was of the same order of accuracy. In view of the mathematical difficulties no attempt is made to improve the theory of the instrument but it is shown that the motion of the disk is nonlinear and that the relation between the period of oscillation and the logarithmic decrement is not that which would be expected on the assumption of simple damped harmonic motion.

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