909 
I have represented the attraction of the separate parts by a (4—#,), 
b—b 
Jo 
0 
but I shall henceforth denote it by « , Which is hardly more 
than a change of a formal nature, required to make @’ retain the 
a” 
character of a pressure on the unity of surface. Just as p + — Is 
ih 
a pressure directed inward on the unity of area, this is the case 
: A = Jo . . 
with « SN and the latter represents the increase of that pressure 
E 0 
in consequence of the mutual attraction of the separate atoms or 
atom groups. It was only after a long hesitation that I dared con- 
clude to this value of the attraction, and when I concluded to it 
it was onlv, to quote Prof. Ricuarps, “with some conviction’. 
It follows from: this form for the attraction that it is equal to 0 
when the atoms touch, and becomes greater when the space allowed 
to the motion of the atoms, increases. Moreover [ put a’ propor- 
tional to the temperature. I must acknowledge that these suppositions 
are not founded on a true insight in the constitution of a complex 
molecule. But I hoped that the study of the consequences of these 
hypotheses which seemed probable to me, and the comparison of 
these consequences with experience might contribute to the know- 
ledge of the properties of such a complex molecule. And so far as 
1 could then compare witli what was known on other grounds, the 
impression I obtained, was not entirely unfavovrable. And now 1 
have been induced to reconsider the conclusion at which I had 
arrived, to see if it leads to the relations which I have drawn up 
in the beginning of this communication. But in this respect I have 
not obtained perfect certainty yet. I have repeatedly discussed some 
difficulties which confronted me, with my son—but these discussions 
have not yet led to an undoubted result. At the moment I shall 
confine myself to communicating the proposed relations. Later we 
hope to be able to derive a rule from, the state of motion of the 
atoms in a molecule, which will perhaps lead to the form: 
when & represents the number of degrees of freedom for the motion 
of the parts of the molecules divided by the number of degreés of 
freedom for the progressive motion of the molecule as a whole, 
viz. 3. From this would follow f == 6,448 for 2-atomic substances, 
and f = 7 for triatomic substances, or perhaps this ought to be 
expressed as follows: for molecules with an axis of symmetry 
