52 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVI.) 
2877- If we assume the existence of another typical globe of air (2864.), having a 
higher temperature than the surrounding atmosphere, then its condition will be that 
Fig. 8. 
Fig. 9. 
of a diamagnetic conductor, and will be represented by 
fig. 9 (2807.) ; and it will have power to affect both the 
intensity and the direction of the lines of force, in con- 
formity with the action of the former globe, but in the 
contrary order. As regards the action of these globes, 
consequent upon the direction of the lines of force in and 
about them upon a needle coming within their influence, it may, in part, be repre- 
sented by a magnet placed either in the direction of the needle for the cold globe, 
or in the reverse direction for the warm one ; but as the lines of force of the combined 
system of the earth and such a magnet are very different in their arrangement to the 
lines of the earth affected by masses of warm or cold air having only conduction pola- 
rity (2820.), it would be too much to say that they correspond, or that the effects on 
the intensity or direction would be the same for similar distance from the centre of 
the globe of air and the representative magnet. 
2878. In endeavouring to proceed, from these hypothetical and comparatively 
simple cases, which are given only to lead the mind on from the results of experiment 
to the supposed condition of matters as regards our atmosphere and the earth, we 
have to consider, that though there will be an effect, and though the intensity and 
direction of the magnetic force, upon the surface of the earth, must vary with changes 
of temperature and density of the atmosphere, still it will be in a manner very 
different from that represented by the typical globe of air, for the latter is a case 
which will never occur, though the variations of the natural case are almost infinite. 
Still the comparison holds in principle, and we may expect that as the sun leaves us 
on the west, some effect, correspondent to that of the approach of a body of cold air 
from the east, will be produced, which will increase and then diminish, and be followed 
by another series of effects as the sun rises again and brings warm air with him. 
2879. The atmosphere diminishes in density upwards, and that diminution will 
affect the transmission of the magnetic force, but as far as it is constant, the effect 
produced by it will be constant too. The portion of the atmosphere which lies under 
the heating influence of the sun, as compared to its depth, will more resemble a slice 
of air wrapped round the earth than a globe. Still the inflection of the lines of force, 
both above and below this stratum, will occur, extending into space above and into the 
earth beneath (2848.), according to the known influence of magnetic power and its 
perfectly definite character (2809.). We are placed at the bottom of this layer of air, 
but as the atmosphere is denser there than higher up, and is also in many cases more 
affected there by changes of temperature, we are probably in a position where the 
inflections and variations due to the assumed causes exist in a considerable degree. 
2880. There are innumerable circumstances that will break up, more or less, any 
