( 377 ) 



been put together we found : 



H, = 1093.10 mm. 

 whereas at the beginning of the two following periods of observation 

 was found : 



on Oct. J 3th '05 i/„ = 1092.11 mm. 



on Febr. 26'^ '06 ^„ = 1091.93 mm. 



The determinations before and after every period of observation 

 give but slight diiferences when compared. A^ a rule the pressure 

 decreases slightly as in the second of the above-mentioned periods of 

 observation (March 7^^ '06, H^ = 1091.83 mm.), sometimes there is 

 a slight increase, as in the first period of observation (Nov. 2"^ '05, 

 Hq = 1092.23 mm.) after observations under low pressure. Before 

 and after the last series of observations, when shortly after the 

 thermometer had been filled with distilled hydrogen, determinations 

 were made at — 183° and — 217°, this difference was particularly 

 large. The zero point pressure after the measurements was then 

 0.33 mm. larger than before them. 



From earlier observations made with another thermometer the 

 same thing appeared. 



Thus on Nov. Id'^ '02 



Ho = 1056.04 mm. 

 was found, and the pressure on June 8^^ '04 was 



Ho = 1055.43 mm. 

 while during further measurements up to July 7'^ '04 the pressure 

 retained a value which within the limits of the errors of observation 

 remained equal to this. 



Chappuis^) found a similar decrease viz. 0.1 mm. in three months 

 with a zero point pressure of 1 M. of mercury. 



Finally a decrease of the normal volume was observed by Kuenen 

 and RoBSON and by Keesom also with the air manometer (see 

 Comm. N". 88 (Oct. 1903) III § 3). The same phenomenon was 

 recently observed with the auxiliary manometer filled with hydrogen 

 mentioned in Comm. N". 78 (March 1902), when it was again 

 compared with the open standard manometer. This comparison will 

 be discussed in a following Communication. 



The possibility of there being a leak is excluded by the fact that 

 a final condition is reached with the thermometer. 



It lies to hand to attribute the variations of the zero point to an 



1) Nouvelles eludes sur les Ihennomètres a gaz, Travaux et Mémoires du Bureau 

 International. T. XIII p. 32. 



