454 M. Haidinger on the Original Formation of Aerolites. 



our globe by a solid crust of 5 German miles thick, would require 

 in the Moon a crust of 32^ miles in thickness, and in the Sun 

 a crust of only T 3 r of a mile thick, or 4235 feet. 



Original pressure takes place only so long as a body is not 

 completely solidified ; from that moment perfect equilibrium is 

 established within it ; pressure, however, must again take place 

 whenever change of temperature modifies the state of rigidity. 

 A rigid body is always apt to conduct heat. That kind of heat 

 whose laws of increase we have to deal with while pursuing in- 

 vestigations on the central heat of the Earth, is conducted heat, 

 transmitted from heat generated, or existing, at greater depths, as 

 more immediately shown by volcanic eruptions. In the regions 

 where volcanic vents open in great numbers on the surface, "the 

 smelted interior of our planet," as Humboldt emphatically says, 

 "stands most in permanent communication with the atmo- 

 sphere." In our times this region is a zone between 75° W. and 

 125° E. long, of Paris, and 47° S. to 66° N. lat., running N.W. 

 in the western portion of the Southern Ocean*. It deserves 

 consideration, that the whole continent of the Old World lies 

 westward of this zone, separated from it towards the south-west 

 only by the Indian Ocean, offering eastwards (as in the Southern 

 Ocean itself) considerable "areas of subsidencef/' and that 

 towards the east of the Southern Ocean the American continent 

 is again fringed with a series of active volcanoes. A remarkable 

 connexion exists between these circumstances and the fact that 

 the altitude of atmospheric strata at the same time rapidly de- 

 creases as we approach the antarctic pole, — just as though a mass 

 of solid highlands had in those parts pressed on the interior of 

 the globe at some early period of its existence, and the terrestrial 

 crust had been broken, and its parts mutually dislocated into the 

 general and more marked outlines now visible on its surface. 

 Should the solidification of the crust proceed so far as to become 

 stationary before the particles of primitive cosmical matter en- 

 closed in it have completed their approximation, these might 

 indeed commence a new and independent process of formation, 

 giving rise to a second shell concentric with the first or external 

 one, and enclosing another internal focus of volcanic activity, the 

 primitive one having become meanwhile extinct. 



If the sum of 65 miles, expressing the thickness of the 

 Moon's crust taken double, is subtracted from her diameter 

 ( = T% 6 im of tne Earth's), and with a density of about 337 J, 



* Physical, und geognost. Erinnerungen. Reise der Novara urn die Erde, 

 p. 20. 



t See Darwin's ' Theory of the Formation of Coral Reefs.' Humboldt, 

 loc. cit. 



% Arago's 'Popular Astronomy,' translated by Hank el, vol. iv. p. 35. 



