ON THE POLARITY OF THE DIAMAGNETIC FORCE. 
247 
On comparing these numbers with those already obtained with bismuth, we observe 
that for like positions the actions of both metals are alike in direction. We further 
observe that the results are determined, not by the relative conductive powers of the 
two metals, but by their relative diamagnetic powers. If the former were the deter- 
mining cause, we should have greater deflections than with the bismuth, which is 
not the case ; if the latter, we should have less deflections, which is the case. 
The third and severest condition proposed by those who object to the experiments 
of M. Weber is to substitute insulators for conductors. I call this condition severe 
for the following reasons ; — according to the experiments of Faraday*, when bismuth 
and sulphur are submitted to the same magnetic force, the repulsion of the former 
being expressed by the number 1968, that of the latter will be expressed by 118. 
Hence an action which, with the means hitherto used, was difficult of detection in 
the case of bismuth, must wholly escape observation in the case of sulphur, the 
’ntensity of whose excitement is nearly twenty times less. The same renmrks apply, 
in a great measure, to all other insulators. 
But the admirable apparatus made use of in this investigation has enabled me to 
satisfy this condition also. To Mr. Faraday I am indebted for the loan of two prisms 
of the self-same heavy glass with which he made the discovery of diamagnetism. 
The bismuth cylinders were withdrawn from the helices and the prisms of glass put in 
their places. It was now necessary to have a perfectly steady magnet, the expected 
result being so small as to be readily masked by, or confounded with, a motion arising 
from some extraneous disturbance. The feeble warmth developed in the helices by a 
current from two cells I found able to create air currents of sufficient power to defeat 
all attempts to obtain the pure action of the prisms. To break up these currents I 
stuffed all unfilled spaces of the box with old newspapers, and found the expedient 
to answer perfectly. With a fresh battery, which delivered a constant stream through- 
out the duration of an experiment, the magnet was admirably steady -f-, and under these 
favourable conditions the following results were obtained : — 
VII. 
Prisms of Heavy Glass, 
length 3 inches, 
width 0‘6. 
depth 0‘5. 
Current direct. 
Position 1. 664 
Position 2. 662 
Position 3. 660 
* Proceedings of the Royal Institution, 1853, p. 5. 
t It was necessary however to select a portion of the day when Albemarle Street was free from cabs and car- 
riages, as the shaking of the entire building, by the rolling of these vehicles, rendered the magnets unsteady. 
2 K 2 
