423 
ce. On moving the log By, log 7-diagram for H, over the #,, 
log hv-diagram, which I shall refer to henceforth as the diagram 
for constant doublets, it was found that comparatively good coinci- 
dence was obtained at temperatures above the BoyLur point, see 
Fig. 2. At temperatures below the Borre point, differences, which 
begin to be noticeable even at the point —164°C. still above the 
Borre point, become very marked, so that below a certain tempe- 
rature not even local coincidence (contact between the two curves) 
can be obtained. 
If we look upon these differences at the lower temperatures as a 
consequence of a deviation, which increases regularly towards those 
temperatures, of the behaviour of the H,-molecules from that which 
is assumed in the hypotheses from which the constant doublets 
diagram is constructed, there is then reason for superposing the 
diagrams in a manner slightly different from that shown in Fig. 2, 
viz. so that the points indicating the highest observed temperatures 
should lie upon the curve of constant doublets. The log Ly, log 7-dia- 
gram does then, in fact, exhibit a deviation from the constant 
doublets diagram, increasing regularly towards the lower tempera- 
tures, and already appreciable at — 139°C. At higher temperatures 
as far as the observations extend, that is, up to 100° C., and taking 
into account the accuracy with which B can be deduced from the 
observations, we may say that as far as B is concerned the thermal 
behaviour of hydrogen in the planetary gas state may be represented 
by that of a system of rigid spheres of central structure, each with 
an electric doublet of constant moment at tts centre. The caloric 
behaviour of H,, in which differences clearly occur earlier, is, to a 
first approximation, consistent with this at the higher temperatures 
of the region under consideration. 
From this method of superposing the diagrams we may easily 
deduce values of o, the diameter of a molecule, and of v, the 
potential energy (v being O for r ==) of two molecules in contact, 
when the axes of the doublets are respectively parallel and perpen- 
dicular to the line joining the centres of the molecules (cf. Suppl. 
N°. 245 § 6). On superposing them so that the H,-points for the 
highest three temperatures fell upon the line for constant doublets, 
then the point log hv = 0,2, /,—=9,7—10 coincided with the point 
log T = 2,075, log By = 6,540—-10. From this, together with the value 
kp = 1,21 .10—'¢ (Suppl. N°. 23, note 174) taken from Perrrin’s 
observations we obtain 
wv = 2,28. 10—4 [erg]. 
From this too, we get for four times the molecules own volume 
