The Bakerian Lecture: On the viscosity or internal friction of air and other gases

All bodies which are capable of having their form indefinitely altered, and which resist the change of form with a force depending on the rate of deformation, may be called Viscous Bodies. Taking tar or treacle as an instance in which both the change of form and the resistance opposed to it are easily observed, we may pass in one direction through the series of soft solids up to the materials commonly supposed to be most unyielding, such as glass and steel, and in the other direction through the series of liquids of various degrees of mobility id the gases, of which oxygen is the most viscous, and hydrogen the least. The viscosity of elastic solids has been investigated by M. F. Kohlrausch and Professor W. Thomson; that of gases by Professor Stokes, M. O. E. Meyer, and Mr. Graham.