76 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVI.) 
2958. Can the magnetic storms of Humboldt be due to atmospheric changes ? This 
is a question on which I would offer the following observations. Supposing a mag- 
netic rest in the atmosphere, and that all local or irregular variations remained un- 
changed for the time, then if a change happened in one place it would be felt instantly 
everywhere else over the whole earth, and in proportion to the distance from the 
place of change. It would be felt instantly, because the impulse would not be con- 
veyed chiefly or importantly through the matter of the earth or air, but through the 
space above, for the lines there are affected by changes in that part of them which 
passes through the atmosphere, and, as I conceive, would affect the other lines in space 
round our globe, which would in turn affect those parts of their lines, which, passing 
downwards to the earth, govern the needles below. In space, I conceive that the mag- 
netic lines offeree, not being dependent on or associated with matter (2787. 2917-), 
would have their changes transmitted with the velocity of light, or even with that higher 
velocity or instantaneity which we suppose to belong to the lines of gravitating force, 
and if so, then a magnetic disturbance at one place would be felt instantaneously 
over the whole globe. 
2959. But the difficulty is to conceive an atmospheric change sufficiently extensive 
and sudden to make itself perceived everywhere at the same time amongst the com- 
paratively local variations that are continually occurring. Still, if there were a lull 
in these disturbances by the opposition of contrary actions or otherwise for the same 
moment of time at two or more places, those places might show a simultaneous effect 
of disturbance, and that even when the cause might be very little or not at all sensible 
in the place where it occurred. A simultaneous change over an area of 600 or 800 
miles in diameter, might produce less alteration in the middle of that area than at the 
extremities of radii of 1000 miles. 
2960. It becomes a fair question of principle to inquire how far masses of the air 
may be moved by the power of the magnetic force which pervades them. When two 
bulbs of oxygen in different states of density are subjected to a powerful magnet 
with an intense field of force, the mechanical displacement of one by the other is 
most striking. Whether in nature the enormous volumes of air concerned, and the 
difference in intensity of the earth’s magnetic force at the different latitudes where 
these may be supposed to be located, combined with the difference of temperature, 
are suflicient to compensate for the small portions of oxygen in the air and the 
smaller variations in density, is a matter that cannot at present be determined. The 
differential result of motion, as has been shown, is very great where the direct result, 
as of compression, is not merely very small but nothing (2774. 2750.), and the atmo- 
sphere is a region where the differential action of enormous masses is concerned. 
2961. Now in the matter of difference of intensity, Gay-Lussac and Biot conclude 
from their observations*, that the magnetic force is the same at a height of four 
miles as at the surface of the earth. M. Kupffer, however, draws from Gay-Lussac’s 
* Annales de Chimie, An. xiii. vol. lii. p. 86. 
