484 Dr. Travers, Mr. Senter, and Dr. Jaquerod. [June 19. 



<: 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." By 

 Morris W. Travers, D.Sc, Fellow of University College, 

 London, George Senter, B.Sc, and Adrien Jaquerod, D.Sc. 

 Communicated by Professor William Ramsay, F.E.S. Re- 

 ceived June 19 —Read June 19, 1902. 



(Abstract.) 



Part I. — By M. W. Travers, and A. Jaquerod. 



Pressure Coefficients of Hydrogen and Helium. 



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. 



The mercury column and the dead space were enclosed between two 

 parallel glass plates in a water-jacket, the temperature of which could 

 be maintained constant, by means of a rapid current of water, to 

 within 0*02° C. Inequalities in the temperature of the mercury column 

 and dead space, to which the largest errors in such measurements are 

 due, were thus eliminated. 



The scale which formed the first surface of the water-jacket was 

 certainly correct to 0*01 mm. The distances between the surfaces of 

 the mercury menisci and the nearest division of the scale were mea- 

 sured by means of a telescope with an ocular micrometer placed at a 



