( B50 ) 
calculated for the intensity of the magnetization at saturation as 
a function of the temperature corresponded very well with those 
which had been found experimentally for magnetite at temperatures 
above the ordinary. Moreover, the law determining the susceptibility 
above the Curie -point i) * * * v ) developed from the hypothesis of the molecular 
field was found in Curie’s experiments, and in others which will 
soon be published, io be accurate over a temperature range of some 
hundreds of degrees. Finally the sudden changes in the specific heat 
at the CuRiE-point \yere in correspondence with the values calculated 
from magnetic data. But other observations do not correspond so 
well with the theory. Figl, PI. I in which the theoretical curve for 
the change of saturation-magnetization with temperature is shown by 
the full curve a, also shows the experimental results for magnetite, 
and the corresponding curve, b , for nickel*). The last curve is drawn 
to such a scale that the best possible correspondence with the theore¬ 
tical is obtained at the CuRiE-point. In contrast with what was found 
for magnetite, nickel shows a deviation from the theoretical gradually 
increasing over the whole curve. Iron and cobalt behave practically 
the same as nickel. When all this is taken into consideration it is 
seen that the hypothesis of the molecular field is of the nature of a 
working hypothesis; the partial confirmation shows that the hypothesis 
contains a kernel of truth, and from the experimental deviations one 
will have to see how it should be modified or extended while still 
retaining its essential features. 
It is not probable that these modifications will attack the property 
of reacting against the orientation by the magnetic field that has been 
ascribed to the kinetic energy, or that they will come into conflict with 
the manner in which the Maxwell-Boltzmann partition law has been 
employed. Not only are these hypotheses of fundamental import, but 
they are still further forced upon our consideration by the ease with 
which they account for the fact that for paramagnetic substances the 
susceptibility varies inversely as the absolute temperature - an 
experimental law that is one of the most firmly established for a 
number of substances. In their important investigations upon the mag¬ 
netization of the elements, of which an account was given at the last 
i) In fins Communication we shall give the name CWpoint to the temperature 
at which spontaneous ferromagnetism ceases. This is by no means inconsistent 
wth Curie s idea hat the transformation temperature is a function of the strength 
of the field since the temperature at which spontaneous ferromagnetism ceases is 
the temperature obtained by reducing the field to zero. 
? measurements. Accurate'experiment, upon the three 
metals and magnetite are m progress. r 
