162 
DR. M. W. TRAVERS, MR. G. SEXIER, AND DR. A. JAQUEROD 
steady for a length of time amply sufficient for the equalisation of temperature 
thronghont that part of the apparatus which was enclosed within the vacuum 
vessel. 
5. Calculation of the Results. 
The method of calcxdating the temperatures of liquid hydrogen was the same as 
has been described in Part II. of this work. It may be pointed out here that, at very 
low temperatures, the mass of gas in the stem of the thermometer becomes con¬ 
siderable, while the mass of gas in the dead space becomes nearly negligible. Taking 
a specific case :— 
Constant for thermometer.44769 
Pressure of gas in thermometer.55‘0 millims. 
Volume of l)ulli.12 T 8 7 
,, ,, stem. 0'035 
,, ,, dead-space.0'280 
TenqDerature of stem. 30° abs. 
,, ,, dead-space. 288° ,, 
The equation for determining the temperature T now becomes :— 
44769 = 55’0 
^2T87 
T 
+ 
0-03.^ 0-280 ] 
30 288 J ’ 
where the second term within the bracket is equal to 0'0012, and the third term is 
less than O'OOl. In both cases tlie correction is exceedlnglv small. 
O a 
In calculating the volume of tiie bulb, the coefficient of expansion of glass between 
0° and 253° C. was taken as 0’000019 for the followino- reasons:—The coefficient of 
O 
expansion between 0° and 100° C. is 0-0000285, between 0° and — 185° it is 
0-0000218 ; on extrapolation one obtains the value which we have taken for the 
coefficient. The following values for the volume of the bulb at — 253 are calculated 
for dlffierent coefficients :— 
Coefficient. 
Volume. 
0-000019 
25-850 
0-000021 
25-837 
This difference of volume corresponds to a difference of 0-01 in the boiling-point of 
hydrogen. 
