the Thermodynamic Scale of Tempera hire. 311 
Making u-e of the data referred to above, we obtain the 
following values for the constants : — 
Hydrogen. Nitrogen. 
a --00060654 Y -'0018319 V fl 
a, -17378V,, 1-0105 V„ 
a, to'lo-LY: 108 73 V . 
Here V is the volume of 1 gramme of the gas at standard 
temperature and pressure. 
Thermodynamic correction to the Gas- Thermometer. 
In the earlier part of this paper I considered the thermo- 
dynamic correction to the gas-thermometer on the assumption 
that the Joule-Thomson effect could be reproduced with 
sufficient accuracy by an expression of the form 
The algebraic work there given is still applicable, since I 
propose to adhere to the same algebraic formula for the 
Joule-Thomson effect, though with altered values of the 
constants. 
Hydrogen. — The coefficient of increase of pressure at 
constant volume has been carefully investigated by M. (Jbap- 
puis. His measurements are probably the best that have 
yet been published : unfortunately, owing to experimental 
difficulties, there is still an appreciable discordance between 
several of his determinations. As the result of his experi- 
ments conducted at three different times, he gives the 
following numbers for the coefficient : — 
•00366254 with initial pressure 998-9 mm. of mercury. 
•00366296 ., .. ., 1000-5 „ 
•00366217 ., .. .. 1001-1 .. 
See Trav. et Mem. du Bur. Int. xiii. p. 61.) 
Of the three determinations here given the two first were 
made with a reservoir of iridio-platinum. and the third with 
a reservoir of hard glass. The variations in the value of the 
initial pressure are small and may be disregarded for our 
present purpose. I am inclined to place the greatest reliance 
on the last determination, which was made with a reservoir 
of hard glass ; since M. Chappuis himself, in another publi- 
cation, refers to the inconvenience caused by the permeability 
ot metals to hydrogen at high temperatures, and it is quite 
