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



bulbs were made was determined by measuring the contraction of the 

 inner tube of a vacuum vessel, 1000 mm. long, when filled with liquid 

 air. The coefficient between 0° and 100° had been found to be 

 0-0000284; between 0° and - 190° it was 0*0000218. 



The pure hydrogen and helium employed in the thermometric 

 measurements was prepared by methods which are described in the 

 next paper, Part III, Appendices II and III. 



The results of our measurements show that with constant volume 

 thermometers, in which the pressure at the melting point of ice is 

 about 1000 mm., the temperatures between 80° and 90° Abs. on the 

 helium scale are 0°*1 higher than on the hydrogen scale. Olszewski 

 obtained identical readings on the two thermometers. This may be 

 accounted for by the fact that he employed helium from clevite which 

 had only been purified by sparking with oxygen, and which possibly 

 contained a trace of argon or other impurity. Our helium was probably 

 quite pure, as it had been passed through a coil cooled to 15° Abs. in 

 liquid hydrogen, and was therefore a more perfect thermometric 

 substance than that employed by Olszewski. 



This result is further discussed in the full paper. 



The Vapour Pressures of Liquid Oxygen. 



Pressures, Temperatures on Temperatures on 



in millimetres. the hydrogen scale. the helium scale. 



800 90-60° 90-70° 



760 90-10 90-20 



700 89-33 89-43 



600 87-91 88-01 



500 86-29 86-39 



400 84-39 84-49 



300 82-09 82-19 



200 79-07 79-17 



Part III. — Bij M. W. Travers and A. Jaquerod. 



Vapour Pressures of Liquid Hydrogen. 



The liquid hydrogen employed in these investigations was obtained 

 by a method devised by one of us two years ago, and described in 

 the 'Philosophical Magazine,' 1901, vol. 17, p. 412. About 400 c.c. 

 of liquid hydrogen was employed in each of the seven sets of experi- 

 ments, of which the following are the results. After filling the gas- 

 ometer with hydrogen, and collecting the quantity of liquid air 

 (8 litres) necessary to cool the apparatus, this quantity of liquid 

 hydrogen can be obtained in half an hour from the moment at which 

 the operations are commenced. Our experience has shown us that 

 when liquid hydrogen is once obtained, it is much more convenient to 



