359 



probable, that the differences between tlie two methods are acci- 

 dental, due to small differences in purity of the mercury and of 

 the walls of the tube. A further investig-ation is therefore desirable/ 

 as the drop-method, if found trustworthy, is much preferable to the 

 method which depends on the use of different masses. 



For high temperatures with air and for all temperatures with 

 butane the drop-method was the only one that could be used. Tt 

 appeared advisable to use the constants a and b as derived from 

 the first series of the above determinations, because in the measure- 

 ments at 100° and with butane the same quantity of mercury was used. 



After the first series of determinations with air the time of fiow 

 for air in steam of boiling water was measured. In order to get an 

 even temperature it was found necessary to admit steam by means 

 of two flasks one at each end of the vapour jacket. A side-tube in 

 the middle allowed the steam to pass off. When the apparatus was 

 reversed the condensed water could flow out through the same tube. 



As mentioned above the constants « and 6 were determined accord- 

 ing to the drop-method. As the results for air at ordinary tempera- 

 ture were found somewhat uncertain, the following results must also 

 be considered to be only approximately correct. 



Observations at 



100.1° m=1.09 



«12 3 



t 121.9 139.4 161 



The deviation for ,^• = 3 is upwards. 



From ,^• = 1 and x = 1 follows 



a =.122 6 = 118.1. 



The constants a, .135 at 15°.5 and .122 at 100°, thus appear 

 to differ but little, compared to the differences between the obser- 

 vations with a different quantity of mercury. 



We thus find 



^100.1 118.1 



\,., ^^-^^ 



=r= 1.205. 



Corrected for gliding 1.205. 

 Breitenbach') gives ^;,. = .0001807, Kankine'-') i^^^^. = .0001803; 

 Markowski =>) n^^. = .0002212 ; Schierloch ') %^^— .0002218. 



1) Ann. Phys. 5, 166; 1901. 



2) A. 0. Rankine I.e. 



8) H. Markowski, Ann. Phys. (4) 14; 1904. 

 4) J. F. Schierloch, Diss. Halle 1908. 



