50 COSMOS. 



of frozen soil, the phenomenon occurs in an island-like form 

 in the more southern districts, but in general it is entirely- 

 independent of the limits of vegetation, or of the growth of 

 timber. 



It is a very considerable advance in our knowledge, when 

 we are able gradually to arrive at general and sound cosmical 

 views of the relations of temperature of our earth in the 

 northern portions of the old continent, and to recognize the 

 fact that under different meridians the limits of the frozen 

 soil, as well as those of the mean annual temperature and 

 of the growth of trees, are situated at very different lati- 

 tudes ; whence it is obvious that continuous currents of heat 

 must be generated in the interior of our planet. Franklin 

 found in the northwest part of America that the ground was 

 frozen even in the middle of August at a depth of 16 inches ; 

 while Richardson observed, upon a more eastern point of the 

 coast, in 71° 12' lat., that the ice-stratum was thawed in 

 July as low as three feet beneath the herb-covered surface. 

 Would that scientific travelers would afford us more general 

 information regarding the geothermal relations in this part 

 of the earth and in the southern hemisphere ! An insight 

 into the connection of phenomena is the most certain means 

 of leading us to the causes of apparently involved anomalies, 

 and to the comprehension of that which we are apt too 

 hastily to regard as at variance with normal laws. 



c. Magnetic Activity of the Earth in its three 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., p. 176-202; vol. 

 ii., p. 333-336 ; and vol. iv., p. 82-86.) 



The magnetic constitution of our planet can only be de- 

 duced from the many and various manifestations of terres- 

 trial force in as far as it presents measurable relations in 

 space and time. These manifestations have the peculiar 

 property 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 



