Magnetic Susceptibility of Alloys of Bismuth and Tin. 49 
(ec) Boltzmann’s assumption, the condition of independence, 
is not mathematically possible, at least as an accurate propo- 
sition. I think there exists at present no theorem satisfying 
the necessary conditions. 
19. Does not the theory of a general tendency of entropy 
to diminish take too much for granted? To a certain extent 
it is supported by experimental evidence. We must accept 
such evidence as far as it goes and no further. We have no 
right to supplement it by a large draft on the scientific 
imagination. 
V. The Magnetic Susceptibility of Alloys of Bismuth and 
Tin. By 8. C. Laws, B.A., B.Sc, St. John’s College, 
Cambridge, “1851 Exhibition” Scholar *. 
N the conclusion of some experiments on the Thomson 
effect in alloys of bismuth and tin, it was thought 
desirable to make further use of the specimens employed in 
that investigation in order to obtain some information con- 
cerning the magnetic behaviour of the alloys. The present 
paper contains the results of experiments made to determine 
the magnetic susceptibility of these alloys. 
The method employed involves the measurement of the 
mechanical force acting on a cylinder of the substance, 
arranged along the axis of a coil of wire, when a current 
passes through this, the cylindrical rod of metal being 
situated partly within and partly without the coil. Boltz- 
mann + has shown ‘how to calculate this force in terms of the 
susceptibility 4, the dimensions of the coil and cylinder, and 
the current passing. The expression obtained becomes much 
simpler when the length of rod within the coil is equal to 
that projecting outside ; accordingly, this has always been 
arranged throughout the experiments. 
Von Httingshausen { has previously utilized this method 
for determining the magnetic susceptibility of bismuth. In 
his experiments the rod of metal was arranged horizontally 
at one end of a light horizontal beam suspended by a fine 
metal wire and provided with a counterpoise at the other 
end ; the force acting on the metal cylinder when a current 
was sent through the coil was then known from the torsion 
produced in the suspending wire. 
Von Httingshausen also used three other distinct methods 
* Communicated by Prof. J. J. Thomson, F.R.S8. 
+ Boltzmann, Wien. Ber. \xxx. p. 687 (1879). 
t Von Ettingshausen, Wied. Ann. xvii. p. 287 (1882). 
Phil. Mag. 8. 6. Vol. 8. No. 48. July 1904. E 
