344 MAGNETIC STORMS. SECT. XXXIV. 



day and night ; the other being a mean annual and diurnal 

 variation proved by General Sabine to exist in those great mag- 

 netic storms or casual disturbances which affect the magnetic 

 elements simultaneously over enormously extensive tracts of the 

 globe. 



Moreover the General discovered that, besides these annual 

 and diurnal variations, the magnetic storms have a variation 

 which accomplishes its vicissitudes in ten or more nearly eleven 

 years, the increase from year to year being gradual, till its 

 maximum becomes twice as great as its minimum value. In 

 consequence of this inequality in the storms or casual disturb- 

 ances, each of the magnetic elements has a variation of similar 

 period and similar maxima and minima. Now the number and 

 magnitude of the spots on the sun had been observed by M. 

 Schwabe, of Dessau, to increase to a maximum, and decrease 

 again to a minimum, regularly in the very same period of between 

 ten and eleven years ; and General Sabine found that this 

 variation in the solar spots, and that in the magnetic elements, 

 not only have the same periods of maxima and minima, but 

 that they correspond in all their minutest vicissitudes. Thus a 

 very remarkable and unexpected connexion exists between ter- 

 restrial and solar magnetism. The dual and antagonist principle 

 is perfectly maintained in the earth's magnetism, all the pheno- 

 mena and their variations being in opposite directions in the 

 two hemispheres. (N. 226.) 



No doubt the magnetic lines of force in the earth are closed 

 curves, as in artificial magnets ; but in their circuitous courses 

 they may extend to any distance in space, or rather in the 

 ethereal medium, even to thousands or tens of thousands of 

 miles ; for the ethereal medium is permeable to lines of magnetic 

 force, or rather transmits them, otherwise the solar spots could 

 not affect the variations of terrestrial magnetism ; besides, they 

 pass through the Torricellian vacuum, which is nearly a void 

 with respect to air, but not to the ethereal medium. 



The atmosphere which surrounds the earth to the height of 

 about fifty miles with sensible density, consists of three and a 

 half parts by weight of nitrogen gas and one part of oxygen, 

 uniformly mixed. The nitrogen is neutral whether dense or 

 rare, hot or cold, while the oxygen is highly paramagnetic ; but 

 it loses a great part of its force when rarefied by heat ; conse- 



