8 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
be exhibited by gases ; and also that in their production the gases differed very much 
one from another*; so that, taking common air, for instance, as a standard, nitrogen, 
and many other gases, were strongly diamagnetic in relation to it, whilst oxygen took 
on the appearance of a magnetic body ; for they were repelled from, while it was at- 
tracted to, the place of maximum force in the magnetic field. 
2721. Recalling the general law given respecting the action of magnetic and dia- 
magnetic bodies (2267, 2418), namely, that the former tended to go from weaker to 
stronger places, and the latter from stronger to weaker places of magnetic power, and 
applying it to such bodies as the gases, which are at the same time both highly elastic 
and easily changed in bulk by the superaddition of very small degrees of force, it 
would seem to follow, that if the particles of a diamagnetic gas tended to go from 
strong to weak places of action, in consequence of the direct and immediate effect 
of the magnetic power on them, then such a gas should tend to become enlarged or 
expanded in the magnetic field. For the amount of power by which the particles would 
tend to recede from the axis of the magnetic field, would be added to the expansive 
force by which they before resisted the pressure of the atmosphere ; that pressure 
would therefore be in part sustained by the new force, and expansion would of neces- 
sity be the result. On the other hand, if a gas were magnetic (as for instance oxygen), 
then the force cast upon the particles, by such a direct and immediate action of the 
magnetic power upon them, would urge them towards the axis of the magnetic field, 
and so coinciding with, and being superadded to the pressure of the atmosphere, 
would tend to cause contraction and diminution of bulk. 
2722. If such supposititious cases were to prove true, we should then be able to 
arrive at the knowledge of the real zero-point (2416, 2432, 2440) -f-, not amongst 
gases only, but amongst all bodies, and should be able to tell whether such a gas as 
oxygen were a magnetic or a diamagnetic body, and also able to range individual 
gases and other substances in their proper places. And though I had originally 
endeavoured to ascertain whether there was any change in the bulk of air in the 
magnetic field, and found none, still Plucker’s statement that he has obtained such 
an effect;}:, and the great enlargement of knowledge respecting the gases which since 
then we have acquired relating to their diamagnetic relations, and especially of the 
great difference which exists between them, encouraged me to proceed. 
2723. I first endeavoured to determine whether there was any affection of the layer 
of air (or other gas) immediately in contact with the magnetic pole, which, either by 
the consequent expansion or contraction of that layer, could render it able to affect 
the course of a ray of light and thus make manifest the changes occurring within. A 
metal screen, with a pin-hole in it, was set up before the flame of a bright lamp in a 
dark room, and thus an artificial star or small definite luminous object was formed. 
* Philosophical Magazine, 1847, vol. xxxi. p. 409. 
X Annales de Chimie, 1850, xxix. p. 134. 
t Ibid. p. 420. 
