ATMOSPHERIC MAGNETISM. 
43 
character, by variations in its physical conditions of temperature and condensation 
or rarefaction (2780.), and at the same time subject to these physical changes in a 
high degree, by annual and diurnal variations, in its relation to the sun, without 
being persuaded that it must have much to do with the disposition of the magnetic 
forces upon the surface of the earth (2796.), and may perhaps account for a large part 
of the annual, diurnal and irregular variations, for short periods, which are found to 
occur in relation to that power. I cannot pretend to discuss this great question with 
much understanding, seeing that I have very little of that special knowledge which 
has been accumulated by the exertions of the great and distinguished labourers, Hum- 
boldt, Hanstebn, Arago, Gauss, Sabine, and many others, who have wrought so 
zealously at terrestrial magnetism over the surface of the whole earth. But as it has 
fallen to my lot to introduce certain fundamental physical facts, and as I have natu- 
rally thought much upon the general principles which tend to establish their relation 
to the magnetic actions of the atmosphere, I maybe allowed to state these principles 
as well as I can, that others may be placed in possession of the subject. If the prin- 
ciples are right, they will soon find their special application to magnetic phenomena 
as they occur at various parts of the globe. 
2848. The earth presents us with a spheroidal body, which, consisting of both para- 
magnetic and diamagnetic substances, disposed with much irregularity as regards its 
large divisions of earth and ocean, are also equally irregularly disposed and inter- 
mingled in its smaller portions. Nevertheless it is, on the whole, a magnet, and, as 
far as we at this moment are concerned, an original source of that power. And 
Rive, founded upon the idea of thermo-electric currents in the atmosphere and earth ; it will be found in a 
memoir entitled ‘ On the Diurnal Variation of the Magnetic Needle.’ Annales de Chimie, 1849, xxv. p. 310. 
A friend has recently called my attention to an observation by M. E. Becquerel, which has reference to the 
present subject, and is in the following words. “ If we reflect that the earth is encompassed by a mass of air, 
equivalent in weight to a layer of mercury of 30 inches, we may inquire whether such a mass of magnetic gas, 
continually agitated and submitted to the regular and irregular variations of pressure and temperature, does not 
intervene in some of the phenomena dependent on terrestrial magnetism. If we calculate in fact what is the 
magnetic force of this fluid mass, we find that it is equivalent to an immense plate of iron, of a thickness a little 
more than -jlgth of a millimetre of diameter (?), and which covers the whole surface of the globe.” This passage 
is at pp. 341, 342 of vol. xxviii. Annales de Chimie, 1850, being contained in an excellent memoir, in which 
the author has well worked out those differential actions of different media, which I developed generally 
years ago. Experimental Researches, 2357. 2361. 2406. 2414. 2423. &c. By such means he has rediscovered 
the magnetic character of oxygen and taken measurements of its force, being evidently unacquainted with the 
account that I gave of this substance in relation to nitrogen and other gases three years ago, in a letter published 
in the Philosophical Magazine for 1847, vol. xxxi. p. 401, and also in Poggendorff’s Annalen and elsewhere ; — 
hence the observations above. I cannot wonder at this, for I myself was not aware of M. E. Becquerel’s paper 
until very lately. In my letter of 1847, I speak of oxygen as being magnetic in common air, p. 410 ; in car- 
bonic acid, p. 414 ; in coal-gas, p. 415 ; in hydrogen, p. 415, its power then being equal to its gravity. I say 
that air owes its place to the oxygen and nitrogen in it, p. 416, and tried to separate these constituents by at- 
tracting the oxygen and repelling the nitrogen. At the end of the paper I hesitate in deciding where the true 
zero between magnetic and diamagnetic bodies is to be placed, and refer to the atmosphere as being liable to 
affections under the magnetic influence of the earth. It was these old results which led me on to the present 
researches. M. F.— Nov. 28, 1850. 
G 2 
