A NEW FORM OF GAS THERMOMETER FOR USE AT VERY LOW TEMPERATURES

Abstract

A new form of helium gas thermometer is described, which is designed for permanent installation in low temperature equipment in order to cover the difficult region between the temperatures of liquid hydrogen and of liquid helium. The device departs radically from the usual gas thermometer practice by having the volume of gas which remains at room temperature considerably larger than that of the thermometer bulb proper. It is shown theoretically that by this means the sensitivity, as compared with that of an ordinary gas thermometer with the same initial pressure and temperature, is greatly increased at the lowest temperatures. Thus it is possible to construct a thermometer which is sufficiently sensitive in the region below 20° K. to read temperatures to within 0.1° with the aid of an ordinary mercury manometer, and yet have a pressure only of the order of one atmosphere at room temperature. An experimental test has shown that the device is entirely practicable.