( 873 ) 
a value of —79° C. for the inversion point; but in his calculation 
he seems to have taken no account of the influence of initial pressure 
and his result is valid only for | atmosphere. 
The results obtained by Ornszewski for air and nitrogen are in 
marked contrast to those here obtained for hydrogen. The diagrams 
by which he shows graphically the relation between inversion- 
temperature and pressure, are lines that are strongly curved, and 
they exhibit, moreover, an inversion temperature increasing with 
increasing initial pressure. The calculations given above throw some 
doubt upon these results. For Joure and Kervin found for air at 
ordinary temperatures a linear relation between cooling-effect and 
pressure difference; this, compared with the foregoing result for 
hydrogen at — 215° C. renders it highly probable that air and hydrogen 
follow the law of corresponding states in the JouLE-KELVvIN effect, 
as was to be expected from the facts that their equation of state 
follows that law, and that both gases are bi-atomic without any 
chemical complication in the molecule‘). 
Keeping in view this thermodynamic similarity of hydrogen with air 
or nitrogen it may be inferred from equations (4) or (5) that the 
inversion temperature curves for all three gases must have the same 
general properties, and exhibit a relation between inversion temperature 
and pressure approximately linear; and it can be seen that the small 
uncertainty in the changes of specific heat with temperature for the 
different gases cannot account for Orszewskr's finding an opposite 
effect of initial pressure. 
Thus we must conclude that expansion through a reduction-valve 
of the same construction as that used by O1szewskr does not satisfy 
the conditions embodied in equations (3) and (15) governing a 
process at the beginning and end of which the enthalpy has the 
same value. 
A subsequent paper dealing with the experimental portion of this 
research will show that the cause of this discrepancy can lie in the 
conditions under which the expansions in Orszewskr’s experiments . 
were carried out. 
1) Cf. H. Kamertincu Onnes: Zitt. Versl. Januari 1896, Comm. Phys. Lab. Leiden. 
No. 23. 
Dante, BertueLot: Journ. de Phys. Mars (1903); and 
Epcar BuckincuHam: Bull. Bur. Stand. (3). 2. (1907). 
Sh 
© 
Proceedings Royal Acad. Amsterdam. Vol. XI. 
