13R 
DR. M. W. TRAVERS, MR. G. SEXTER, AND DR. A. JAQUEROD 
3. The Pressure Coefficients of Hydrogen and Helium between 0° and 100° C. 
As has already been pointed out, there is no appreciable difference bet-vveen the 
pressure coefficient of the two gases, which may be considered as approximating 
very closely to 0’003G6255. Tlie reciprocal of this number is 273'03, and though an 
error of 0'01° uidy is incurred by taking 273 as the temperature of melting ice on 
the scale of either thermometer, we have in calculating our results employed the 
true coefficient. 
4. Hie Coefficient o f Expansion of Glass between 16° and — 190° C. 
The coefficient of expansion of the glass was determined in the following manner. 
Tlie inner tube of a cylindrical vacuum vessel, which was 30 millims. wide and 
1000 millims. long, was graduated for short distances close to its two ends. The 
vacuum vessel was enclosed in a water-jacket, and was set up vertically in front of 
two telescopes, of short focus, fitted with micrometer eye-pieces. The cross wires of 
the micrometer eye-pieces Avei'e fii-st brought into coincidence with marks at the two 
ends of the vacuum vessel. The vessel was then filled with liquid air and the 
distances through which the marks on the vacuum vessel moved were observed. 
I’he folloAving result for the volume coefficient is calculated from the linear con¬ 
traction of the glass :— 
f Joefficient of expansion 0° to 100° C. (by weight thermometer) . 0’0000285. 
,, ,, 0° to — ]90°G. (from linear contraction) . 0'0000218. 
5. Method of Experiment. 
In our experiments we liave overcome the difficulty last referred to bv immersing 
our thermometer, together Avith a 1)ulb in Avhich jjure oxygen coidd be liquefied, and 
A\hich was connected with a manometer, in liquid air or oxygen contained in a 
vacuum vessel. The liquid in the vacuum vessel could, if necessary, lie made to boil 
steadily, by passing through it a current of air or hydrogen, and could be maintained 
at a constant temperature by enclosing the vacuum vessel in another vacuum vessel 
of larger dimensions also containing liquid air. Readings of the thermometer and of 
the manometer connected with the bulb containing the pure liquid oxygen were 
taken simultaneously by two observers. 
6. The Large Constant-Volume Hiermometer. 
The thermometer employed in determining the pressure coefficients of h^^drogen 
and helium between 0° and 100° C. has been fully described in the previous memoir 
(.Part 1.). Tl le same instrument, and three others of smaller dimensions, were 
