28 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
orig'inal place, and render it equidistant from the magnetic axis with the vacuum 
tube. In this position the two tubes would, as respects the glass, neutralize each 
other (2775.); and considering the vacuum as zero, the oxygen alone may be con- 
sidered as active, and the force required to hold it out may be looked upon as the 
force with which the oxygen, at that distance of half an inch, tended to go to the 
magnetic axis. The deflection of the glass filament or spring, at the place where the 
oxygen tube was held by it, was rather more than 1 inch from its position when re- 
lieved from the pressure of the tube. Being taken away, it was set up in the horizontal 
position (after being turned 90° on its axis, so that the flexure might be in the same 
direction, relative to the filament, as before) ; and the position of the end being marked, 
weights were put on it at the place of former contact with the oxygen tube, until they 
produced the same amount of deflection as before. It required rather more than the 
tenth of a grain to produce this effect; and this, considering that the whole oxygen 
only weighed OTI7 of a grain, and that no part of it was nearer than half an inch, 
whilst the average distance of the mass was above an inch from the magnetic axis, 
gives a high expression for the magnetic power. 
2796. It is hardly necessary for me to say here that this oxygen cannot exist in 
the atmosphere, exerting such a remarkable and high amount of magnetic force, 
without having a most important influence on the disposition of the magnetism of 
the earth as a planet, especially if it be remembered that its magnetic condition is 
greatly altered by variations in its density (2781.) and by variations in its tempera- 
ture*. I think I see here the real cause of many of the variations of that force, which 
have been, and are now, so carefully watched on different parts of the surface of the 
globe. The daily variation and the annual variation both seem likely to come under 
it; also very many of the irregular continual variations which the photographic pro- 
cess of record renders so beautifully manifest. If such expectations be confirmed, and 
the influence of the atmosphere be found able to produce results like these, then we 
shall probably find a new relation between the aurora borealis and the magnetism of 
the earth, namely, a relation established, more or less, through the air itself in con- 
nexion with the space above it ; and even magnetic relations and variations which 
are not as yet suspected, may be suggested and rendered manifest and measurable, 
in the further development of what I will venture to call Atmospheric Magnetism 
(2847- &c.). I may be over-sanguine in these expectations, but as yet I am sustained in 
them by the apparent reality, simplicity and sufficiency of the cause assumed, as it at 
present appears to my mind. As soon as I have sufficiently submitted these views 
to a close consideration and the test of accordance with observation, and where 
applicable with experiments also, I will do myself the honour to bring them before 
the Royal Society. 
* Philosophical Magazine, 1847, vol. xxxi. p. 417. 
Royal Institution, August 2, 1850. 
