22 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
could not by itself, or with mere air inside, retain it for a moment without the aid of 
considerable restraint. The power with which the tubes only would retain their 
equidistant position, combined with the extent to which they are displaeed from this 
position, shows the great amount of force which this conjoint action of the oxygen 
and the nitrogen leaves free to be exerted in the one direction, namely, from the 
oxygen inwards or axially, for though the action be complicated the result is simple. 
By former experiments, the nitrogen is known to pass equatorially and the oxygen 
axially in air*, and the nitrogen tube will pass equatorially according to a certain dif- 
ferential force, depending on the flint-glass and the nitrogen on the one hand, and 
the bulk of air displaced by them on the other. The oxygen tube in like manner will 
tend to pass axially by a differential force, the amount of which will depend upon the 
tendency of the oxygen to go axially, of its tube to go equatorially, and of their joint 
relation to the air they displace. But both the tubes and their contents are by their 
joint relation to the air and their mechanical connexion so related to each other, that 
when a force (as of torsion) is employed to restore them to their equidistant position 
from the magnetic axis, all consideration of the matter of the tubes and of the air as 
a surrounding medium may be dismissed. The gases within them may be con- 
sidered as in immediate relation with each other and the magnetic axis, and disem- 
barrassed from all other actions : and the force which may be found needful to place 
them equidistant, is the measure of their magnetic or diamagnetic differences. 
2777. Having thus explained the general prineiples of action, I will not at present 
go into their application in the construction of a measuring instrument or the results 
obtained with it, further than is required for the general elucidation of magnetic and 
diamagnetic bodies, and the determination of the true zero-point (2721. 2722.). 
2778. The principles just described enabled me to return to a method of investiga- 
tion whieh on a former occasion greatly excited my hopes (2433.), but which seemed 
then suddenly cut olf by want of power. Various bodies, whether considered as mag- 
netic or diamagnetic substances, admit of two modes of treatment, which promise 
to be exceedingly instruetive as regards their properties and their destined purposes 
in natural operation. A gas may be heated or cooled, and the effect of temperature, 
which is known to be very influential may now be ascertained without any change 
in the bulk of the gas ; or it may be rarejied and conderised through a very extensive 
range, and the effect of this kind of change upon it ascertained independent of tem- 
perature or the presence of any other substance. Solids and liquids do not admit of 
these methods of examination, and do not therefore assist in the determination of 
the zero-point and of the true distinction of magnetic and diamagnetic bodies in the 
same manner that the gases do. 
2779- It appeared to me that if a gaseous body were magnetic, then its magnetic 
properties ought to be diminished in proportion as it was rarefied, i. e. that equal 
volumes of such a gas at different pressures ought to be more magnetic, as they are 
denser; on the other hand, that if a gas were diamagnetic, rarefaction ought to 
* Philosophical Magazine, 1847, vol. xxxi. j). 409. 1' Ibid. pp. 406, 417. 
