Science in Germany

Abstract

(From a German Correspondent) IT is known to have been first discovered theoretically by Maxwell, that the co-efficient of friction of a gas is independent of the pressure. This law has been tested and confirmed by Maxwell and O. E. Meyer, and more recently by Kundt and Warburg (Philosophical Magazine, 4, vol. iv.; and fully in Poggendorff's Annalen, Bd. 155 oand 156) with reference to the sliding of gases in limits between 760 and 1 mm. pressure of mercury. The latter experimenters observed, as Maxwell did, the decrease of vibrations of a round glass disc suspended bifilarly between two fixed plates. At pressures under 1 mm. Kundt and Warburg were unable accurately to investigate the friction. They could perceive, however, that with continued progressive evacuation by the friction apparatus, the damping force exerted by the rarefied gas on the motion of the oscillating disc, decreases; still, even in the best vacuum which could be produced, it had still a considerable value. Thus, e.g., in the best hydrogen vacuum which Kundt and Warburg could produce, the damping force was not less than one-third of the value obtained with full hydrogen-pressure (760 mm. mercury).