24 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
rare oxygen, or a vacuum. This however would imply, that the acting force of a 
substance, as the oxygen, could increase in proportion as the quantity of the sub- 
stance diminished, which is not, I think, a philosophical assumption ; and besides 
that, other reasons will soon appear to show that the magnetic condition which dis- 
appears as the oxygen is removed, belongs to, and is dependent upon that substance, 
and that oxygen is therefore a truly magnetic body. 
2783. Nitrogen, being the other and larger part of the atmosphere, was then sub- 
jected to experiment, and three tubes, one containing the gas at a pressure of 30 
inches of mercury, another with the gas at the pressure of 15 inches, and the third 
reduced as nearly as it could be to a vacuum, were prepared (2780.). When these 
were compared one with another in the magnetic field, they were found to be so 
nearly alike as not to be distinguishable from each other, i. e. they remained equi- 
distant from the magnetic axis. I do not mean to imply that nitrogen at these dif- 
ferent pressures is absolutely the same bulk for bulk (an instrument now under con- 
struction will enable me hereafter to compare and measure with infinitely greater 
accuracy, and to ascertain these points) ; but as compared with oxygen, the great and 
extraordinary differences produced by rarefaction there, have no corresponding dif- 
ferences here. If there are any, they are insensible at present, and may, for the chief 
purpose of this paper and the determination of the zero-point between magnetics and 
diamagnetics, be taken as nothing. 
2784. Nitrogen therefore appears to be neither magnetic nor diamagnetic; if it 
were either, it could not but fall in its specific condition as it was rarefied ; as it is, it 
is equivalent to a vacuum. If a given space be considered as a vacuum, into which 
oxygen or nitrogen is to be gradually introduced, as oxygen is added the space be- 
comes more and more magnetic, i. e. more competent to admit of the kind of action 
distinguished by that word ; but the corresponding gradual addition of nitrogen to 
an empty space produces no effect of that kind, or the contrary, and the nitrogen is 
therefore neither magnetic nor diamagnetic, but like space itself. 
2785. As yet I have found no gas, which, being on the diamagnetic side of zero, 
can at all compare with oxygen in the range of effect produced by rarefaction. For 
the present, I may mention olefiant gas and cyanogen as substances which appear to 
proceed inwards, or towards the axial line, as they are more rarefied. They are 
therefore not merely at zero, but are in opposition to oxygen and are diamagnetic 
bodies. But if we want a body that is strongly and undeniably diamagnetic, and 
which, being added to or introduced into space, will make it diamagnetic, as oxygen 
renders it magnetic, then flint glass or phosphorus presents us with such a sub- 
stance, When these bodies are made into forms similar to the volumes of nitrogen, 
or the vacua in size and shape, and are compared with them on the torsion balance, 
they^pass outwards with much force; and it is probably the great diamagnetic force 
of the glass of the tubes that prevents the effect of rarefaction from being more 
evident in olefiant and other gases. 
2786. When a tube has been filled with a particular gas, then exhausted as much 
