On the measurement of temperature. Part I.—On the pressure coefficients of hydrogen and helium at constant volume and at different initial pressures. Part II.—On the vapour pressures of liquid oxygen at temperatures below its boiling point on the constant volume hydrogen and helium scales. Part III.—On the vapour pressures of liquid hydrogen at temperatures below its boiling point on the constant volume hydrogen and helium scales

The pressure coefficients have been determined by measuring the pressures which the gases exert when the bulb of the thermometer is in melting ice, or in steam at the boiling point. Full details of the method employed are given in the paper of which this is an abstract. The principal new features of the method are as follows:—The gases were introduced into a glass bulb sealed to a capillary glass stem, which was in turn sealed at the other end to the tube which formed the “dead space”; thus eliminating any chance of leakage of the gas, which must necessarily occur when steel tubes, connected to the glass by cement, are employed. The mercury in the dead space was brought close to, but not into contact with, a point in the dead space, and the pressure on the gas in the thermometer was directly observed by measuring the height of the mercury in an exhausted manometer tube above the mercury in the dead space; the apparatus was so arranged that the two mercury menisci lay on the same vertical axis.