498 



in ice. Previously this instrument liad been carefully calibrated with 

 the aid of a set of pipettes with pure helium. We are glad to offer 

 Mr. P. G. Cath our thanks for his assistance in this woi'k. 



4. Results. The thermometers were mounted side by side in the 

 helium-cryostat, which was vigorously sth-red by means of a pump- 

 stirrer. The bulbs were surrounded by brass tubes in order to protect 

 them from radiation through the liquid helium. The vapour pressures 

 of helium were corrected for the aerostatic difference of pressure 

 between tlie helium liquid surface and the \'apour-pressure manometer. 



Two series of observations were made. In the first Mr. Chappuis 

 did us the honour to take part in the measurements. In this series 



