( 597 ) 
4. The same holds for variations of chemical stale (allotropy,. 
One of us in 1900 proposed to call the first of these thermoma"- 
net.c rules Curie’s law and to introduce a Curie’s constant such that: 
X(<? + 278 )=C. 
It was also expressly stated that very probably this was* only a 
kind of “limit-law” in the sense of the analogous law for ideal 
gases. In addition it was very soon shown that the usual theory 
of directed magnecules leads to such a law, when generalised from 
a more magnetokinetic point of view; this was theoretically proved 
and experimentally continued in the Lorektz- and BosscHA-volumes 
of the “Archives ’'). With all due regard for Curie’s important re¬ 
searches and for his first rule, the second can and could have no 
general signification, for it at once contradicted the results of other 
observers, e. g as in the special case of water. 
With regard to the third and fourth rules even their author pointed 
out several exceptions. As the values of the susceptibilities of the dia¬ 
magnetic substances tested proved much less than those of the paramag¬ 
netic bodies, Curie came to the conclusion that these two opposite 
forms of magnetic induction were due to completely different causes. 
Starting from these experimental conclusions, Lamgevin *) in the 
year 1905 elaborated an electronic theory of magnetism; he also 
gave a kinetic representation of Curie’s first law, completely analogous 
to the one mentioned above, without, however, mentioning it, and which 
is in addition perfectly independent of the introduction of electrons. 
It appeared, therefore, desirable to investigate the thermomagnetic 
properties of more substances: in the first place those of elements, 
in order to judge whether Curie’s conclusions admit of such an 
extensive generalisation. It may be at once remarked that such is 
not at all the case. 
Experimental Arrangement. The method, previously used by Curie and 
other investigators, of the torsion-balance combined with a non-uniform 
field was applied, employing the semicircular electromagnet recently 
described in^ these Proceedings. The axes of the two cores formed an 
angle of 10° to 20°; the maximum gradient of the field then lies at 
a certain dist ance to one side of their point of intersection. The field 
) H . dc Bois, Rapp. Gongr. d. Phys. 2 p. 486, Paris 1900. - Arch. Need. 
(2) o p. 246, 1900, also 6. p. 581, 1901. - Verh. nat. en gen. Gongr. 8 p. 60, 
Rotterdam 1901. Notations: P 
a, Atomic weight. I 6, , Temperature. 
C, Curie’s constant. j jr, Specific susceptibility. 
(4) 2> 4 P p L 678 EV 1905 Ann ’ ^ ^ ^ (8) 5 P ‘ 7 °’ 1905 * JourD * dc Pb f s - 
40 * 
