172 COSMOS. 



The figure of the Earth and the amount of solidification 

 (density) which it has acquired are intimately connected with 

 the forces by which it is animated, in so far, at least, as they 

 have been excited or awakened from without, through its 

 planetary position with reference to a luminous central body. 

 Compression, when considered as a consequence of centrifugal 

 force acting on a rotating mass, explains the earlier condition 

 of fluidity of our planet. During the soHdification of this 

 fluid, which is commonly conjectured to have been gaseous 

 and primordially heated to a very high temperature, an enor- 

 mous quantity of latent heat must have been liberated. If 

 the process of solidification began, as Fourier conjectures, by 

 radiation from the cooling surface exposed to the atmosphere, 

 the particles near the center would have continued fluid and 

 hot. As, after long emanation of heat from the center toward 

 the exterior, a stable, condition of the temperature of the 

 Earth would at length be established, it has been assumed 

 that with increasing depth the subterranean heat likewise 

 uninterruptedly increases. The heat of the water which 

 flows from deep borings (Artesian wells), direct experiments 

 regarding the temperature of rocks in mines, but, above all, 

 the volcanic activity of the Earth, shown by the flow of molt- 

 en masses from open fissures, afford unquestionable evidence 

 of this increase for very considerable depths from the upper 

 strata. According to conclusions based certainly upon mere 

 analogies, this increase is probably much greater toward the 

 center. 



That which has been learned by an ingenious analytic cal- 

 culation, expressly perfected for this class of investigations,* 



efter den Latinske original of Jens Baggesen. Holberg, who studied 

 for a time at Oxford, was born at Bergen in 1685, and died in 1754 as 

 Rector of the University of Copenhagen.] — Tr. 



* Here we must notice the admirable analytical labors of Fourier, 

 Biot, Laplace, Poisson, Duhamel, and Lame. In his Thiorie MathSma- 

 tiqufi do la Chaleur, 1835, p. 3, 428-430, 436, and 521-524 (see, also, 

 De la Rive's abstract in the Bibliotheque Universelle de Geneve), Pois- 

 son has developed an hypothesis totally different from Fourier's view 

 ( Theorie Analytique de la Chaleur.) He denies the present fluid state 

 of the Earth's center ; he believes that " in cooling by radiation to the 

 medium sun'ounding the Earth, the parts which were first solidified 

 Bunk, and that by a double descending and ascending current, the great 

 inequality was lessened which would have taken place in a solid body 

 cooling from the surface." It seems more probable to this great ge- 

 ometer that the solidification began in the parts lying nearest to the 

 center : " the phenomenon of the increase of heat with the depth does 

 not extend to the whole mass of the Earth, and is merely a consequence 

 of the motion of our planetary system in space, of which some parts 



