RECAPITULATION. 



are continually manifested. Here is no moderated and regulated 

 temperature, no alternations of light and darkness, no succession 

 of seasons, no varieties of climate, no divisions of land and water. 

 The sun is, in fact, a vast globular furnace, the heat emitted from 

 each square foot of which is seven times greater than the heat 

 which issues from a square foot of the fiercest blast furnace. 

 Such is the intensity of this heat, that although the distance of 

 the earth from the sun is little less than 100,000000 of miles, 

 and although the surface of the earth, by reason of its diurnal 

 rotation, is withdrawn from the sun's olirect influence during 

 alternate intervals of twelve hours, yet the total quantity of heat 

 received by the earth from the sun in a year is sufficient, if uni- 

 formly diffused over its surface, to liquefy a crust of ice covering 

 it 100 feet thick ! 



It follows from this that the average heat received by each 

 square foot of the earth's surface from the sun in a year would 

 be sufficient to dissolve 5400 Ibs. weight of ice. 



How entirely removed from all analogy with the earth such a 

 globe of fire must be, is apparent. 



19. The moon, on the other hand, while it has nothing in 

 common with the sun, is not the less destitute of all those 

 analogies to the earth which suggest habitability. We shall, on 

 another occasion, explain fully the circumstances attending our 

 satellite. For the present, it will be sufficient to observe that it 

 has no atmosphere, no clouds, no water or other liquids, no 

 intervals of light and darkness, bearing any analogy to our days 

 and nights ; that its surface bristles with one unbroken con- 

 tinuity of rugged mountainous region more savage than the 

 glaciers which crown the summits of the Alps, the Andes, or the 

 Cordilleras, and that even in the valleys a temperature must 

 prevail colder than that of our poles. 



It will therefore be easily imagined how little analogy such a 

 globe has to the earth, and how utterly unsuited it would be for 

 the habitation of organised tribes. 



20. Astronomical observation renders it probable that the 

 satellites of the other planets are under physical conditions 

 similar to that of the moon, and that, like the moon, they are 

 deprived of the conditions of habitability. 



21. A numerous class of bodies, called comets, have been proved 

 by modern observation to be connected by gravitation with the 

 solar system. These bodies appear generally to be divested of 

 all solidity, and to be masses of vaporous matter floating through 

 the system. It is obvious that these can have no analogy to the 

 earth. 



In the space between the two groups of planets which present 



63 



