Dr. Faraday on Magnetic and Diamagnetie Action. 239 
2435. Whether the negative results obtained by the use of 
gases and vapors depend upon the smaller quantity of matter in a 
given volume, or whether they are direct consequences of the 
altered physical condition of the substance, isa point of very 
great importance to the theory of magnetism. I have imagined, 
in elucidation of the subject, an experiment with one of M. Cag- 
niard de la Tour’s ether tubes, but expect to find great difficulty 
in.carrying it into execution, chiefly on account of the strength, 
and therefore the mass of the tube necessary to resist the expan- 
. Sigmof the imprisoned heated ether. 
' 2436. The remarkable condition of air and its relation to 
betes taken from the magnetic and diamagnetic. classes, cause 
it to point equatorially in the former and axially in the ee 
Or, if the experiment presents its results under the form of at- 
taction and repulsion, the air moves as if repelled in a magnetic 
medium and attracted in a medium from the diamagnetic class. 
Hence i it seems as if the air were magnetic when compared with 
- diamagnetic bodies, and of the latter class. when compared. to 
wpyiettio bodies. — 
~ 2437.-'This result I have ecinaphcrod as explained by the as- 
sumption that bismuth and its congeners are absolutely repelled 
by the magnetic poles, and would, .if there were nothing else 
Concerned in the phenomena than the magnet and the bismuth, 
beequally. repelled. So also with the iron and its similars, the 
attraction has been assumed as a direct result of the mutual ac- 
tion of them and the magnets; further, these actions have been 
sufficient to account for the pointing of the air both 
axially and equatorially, as also for its apparent attraction and re- 
pulsion ; the effect in these cases being considered as due to the 
‘travelling of the air to those positions seed the magnetic or dia- 
magnetic bodies tended to leave. 
2438. The effects with air are, eiglatinds in these results pre- 
cisely: the same as those which were obtained with the solutions 
of iron of various strength, where all the bodies belonged to the 
magnetic class, and where the effect was evidently due to the 
Steater or smaller degree of magnetic power possessed by the so- 
lutions, A weak solution in a stronger pointed equatorially and 
Was repelled: like a diamagnetic, not because it did not tend by 
Attraction to an axial position, but because it tended to that posi- 
tion-with less force than the matter around it;-so the question 
