60 UR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXI.) 
force passing through them, and the virtual difference in property and character be- 
tween any two substances taken from different places in the list (2424.) will be the 
same; for it is the differential relation of the two which governs their mutual effects. 
2445. It is that group which includes air, gases, vapours, and even a vacuum 
which presents any difficulty to the mind ; but here there is such a wonderful change 
in the physical constitution of the bodies, and such high powers in some respects are 
retained by them, whilst others seem to vanish, that we might almost expect some 
peculiar condition to be assumed in regard to a power so universal as the magnetic 
force. Electric induction being an action through distance, is varied enough 
amongst solid and liquid bodies ; but, when it comes to be exerted in air or gases, 
where it most manifestly exists, it is alike in amount in all (1292.) ; neither does it 
vary in degree in air however rare or dense it may be (1284.). Now magnetic 
action may be considered as a mere function of electric force, and if it should be 
found to correspond with the latter in this particular relation to air, gases, &c., it 
would not excite in my mind any surprise. 
2446. In reference to the manner in which it is possible for electric force, either 
static or dynamic, to be transferred from particle to particle when they are at a 
distance from each other, or across a vacuum, I have nothing to add to what I have 
said before (1614, &c.). The supposition that such can take place, can present 
nothing startling to the mind of those who have endeavoured to comprehend the 
radiation and the conduction of heat under one principle of action. 
2447. When we consider the magnetic condition of the earth as a whole, without 
reference to its possible relation to the sun, and reflect upon the enormous amount 
of diamagnetic matters which, to our knowledge, forms its crust ; and when we 
remember that magnetic curves of a certain amount of force and universal in their 
presence, are passing through these matters and keeping them constantly in that 
state of tension, and therefore of action, which I hope successfully to have developed, 
we cannot doubt but that some great purpose of utility to the system, and us its 
inhabitants, is thereby fulfilled, which now we shall have the pleasure of searching 
out. 
2448. Of the substances which compose the crust of the earth, by far the greater 
portion belongs to the diamagnetic class ; and though ferruginous and other magnetic 
matters, being more energetic in their action, are consequently more striking in their 
phenomena, we should be hasty in assuming that therefore they overrule entirely the 
effect of the former bodies. As regards the ocean, lakes, rivers, and the atmosphere, 
they will exert their peculiar effect almost uninfluenced by any magnetic matter in 
them ; and as respects the rocks and mountains, their diamagnetic influence is per- 
haps greater than might be anticipated. I mentioned that, by adjusting water and 
a salt of iron together, I obtained a solution inactive in air (2422.) ; that is, by a due 
association of the forces of a body from each class, water and a salt of iron, the mag- 
netic force of the latter was entirely counteracted by the diamagnetic force of the 
