f*01 ) 
We have been occupied with another question besides the change 
of specific susceptibility with temperature, which was suggested 
both by the experimental results obtained by Fleming and Dewar 
and by the theories of L angevin and Weiss. 
In the experiments of the first-namqd there appeal’s sufficient 
evidence for the conclusion that there is a decided diminution of the 
susceptibility as the strength of the field increases (the diminution is 
of the order of 10% in a field of 2500 gauss). Now, according to 
the theory of Langevin para-magnetic substances must, it is true, 
exhibit this phenomenon, but calculation from his formulae limits 
the magnitude of this change to less than 0.1% in the case of liquid 
oxygen at its boiling point. Should a higher value than this be 
obtained, then one would be led to assume the existence of a Weiss 
molecular field 1 ). We arranged our experiments so that the liquid 
and the solid oxygen could be subjected to a field of 16000 gauss, 
a field very much stronger (about six times) than that used by 
Fleming and Dewar, so that we might expect the phenomenon which 
appeared in the course of their experiments to be exhibited to a 
much greater degree in ours even at the same temperatures as were 
used by them. If what was observed by Fleming and Dewar could 
really be . ascribed to the beginning of saturation then the theory 
would further lead us to expect that as the temperature sank the 
change would strongly increase (becoming infinite at T = 0), and 
that in our experiments with liquid hydrogen it would-become very 
striking. We have, however, observed only small deviations, which 
we shall discuss further in $ 5. 
As regards the experimental methods employed by us in our in¬ 
vestigation, two completely different schemes were adopted: on the 
one hand was measured the magnetic attraction exerted upon a 
column of the liquid, and on the other the maximum couple 
exerted by a homogeneous field upon an ellipsoid. The second method 
is more especially suitable for comparative measurements and can also 
be used for frozen oxygen; the first can be used only for the liquid 
phase, but on the other hand it makes very trustworthy absolute 
measurements possible; we have therefore adopted it as the basis of 
our other measurements. In the carrying-out of each method further 
precautions are still desirable, so that while we are busy pushing 
on the investigation, we propose at the same time to repeat it in 
part in order to increase the accuracy of the results obtained by 
taking such further precautions as have appeared possible in the 
course of the work. 
x ) Weiss, L’hyp. du champ mol6c. loe. cit 
