I. The expansion of argon and of helium as compared with that of air and hydrogen

Accurate comparisons of temperatures, as read with the aid of thermometers filled with different gases, have not often been made. The history of the subject may be said to have begun with the classical researches of Regnault. Of recent work of this kind, that of Chappuis was performed entirely at temperatures below 100°, the gases employed being hydrogen, nitrogen, and carbon dioxide. The experiments of Grunmach and Pernet were also conducted at temperatures below 100°. Crafts has compared the readings of a number of mercury thermometers with those obtained by Regnault and by himself with a hydrogen thermometer.