993 



investigation regarding the vapour-pressnre of lij'drogen above tlie 

 boiling point; if the coininnnications qnoted above are consulted, 

 tig. 1 and, as regards tiie thermometer, figg. 3 and 4 will not require 

 much explanation. ') 



At pressures above and below one atmosphere the mercury surface 

 can now be read in one and the same tube I'a^ "). By tap /v6>^ a 

 vacuum can be produced above I'a^ which is kept up by means 

 of Dewar's metliod of charcoal cooled in liquid air with K0^ and 

 KSro open and KS^ closed. For press ure- readings above one 

 atmosphere KO^ is connected with a barometer and a space of 

 constant and practicallj atmospheric pressure in the same manner 

 as with the previous thermometer. (See fig. 1). 



Fig. 1. 



1) The letters in fig 3 are the same as those in tiie previous communications; 

 modified parts are indicated by a dash or an additional dash. 



~) At the time wlien the previous type of thermometer used in the latest 

 experiments (Comm. 141 Proc. May 1 91 4) was constructed, it was not possible to pro- 

 vide for a practically complete vacuum, with tlie same degree of certainty as at present. 



