49 



c. Magnetic Activity of the Earth in its tliree Manifestations 

 of Force Intensity, Inclination, and Variation. Points 

 (called the Magnetic Poles), in which the Inclination is 90. 

 Curves on which no Inclination is observed (Magnetic 

 Equator). The Four different Maxima of Intensity. 

 Curve of weakest Intensity. Extraordinary Disturbances of 

 the Declination (Magnetic Storms). Polar Light. 



(Extension of the Picture of Nature, Cosmos, vol. i. pp. 169 

 197, vol. ii. pp. 717720, and vol. iv. pp. 394398.) 



The magnetic constitution of our planet can only be 

 deduced from the many and various manifestations of ter- 

 restrial force in as far as it presents measureable relations in 

 space acd time. These manifestations have the peculiar pro- 

 perty of exhibiting perpetual variability of phenomena to a 

 much higher degree even than the temperature, gaseous 

 admixture, and electrical tension of the lower strata of the 

 atmosphere. Such a constant change in the nearly allied 

 magnetic and electrical conditions of matter moreover essen- 

 tially distinguishes the phenomena of electro-magnetism 

 from those which are influenced by the primitive funda- 

 mental force of matter its molecular attraction and the 

 attraction of masses at definite distances. To establish 

 laws in that which is ever varying, is however the highest 

 object of every investigation of a physical force. Although 

 it has been shown by the labours of Coulomb and Arago 

 that the electro-magnetic process may be excited in the 

 most various substances, it has nevertheless been proved 

 by Faraday's brilliant discovery of diamagnetism, (by the 

 differences of the direction of the axes, whether they incline 

 north and south, or east and west,) 'hat the heterogeneity of 

 matter exerts an influence distinct from the attraction of 

 masses. Oxygen gas, when inclosed in a thin glass tube, will 

 show itself under the action of a magnet to be paramagnetic, 

 inclining north and south like iron ; and while nitrogen, 

 hydrogen, and carbonic acid gases remain unaffected, phos- 

 phorus, leather, and wood show themselves to be diamag- 

 netic, and arrange themselves equatorially from east to west, 



voi* v. K 



