CHAPTER VII 



THE ATMOSPHERE 



THE conception of Laplace has been generally accepted that the 

 solar system arose as a condensation from a vast nebula of gaseous 

 matter, a nebula such as may be seen in various parts of the 

 heavens at the present day. This nebula, by radiating its heat 

 into space, cooled and contracted in volume, and in so doing threw 

 off rings of vapour at various stages. These rings by the action 

 of gravity and centrifugal force became moulded into planets. 



The earth, intensely heated by the latent heat set free in 

 .the process of condensation, first appeared as a luminous mass 

 surrounded by an atmosphere of metallic vapour " vapours 

 which condensed and fell and boiled off again on touching the 

 hot surface." In the infinity of time the crust of the earth 

 cooled, the metallic vapours condensed into solid earth, the 

 atmosphere cleared, and finally, but under vastly different con- 

 ditions to the present, conditions of heat, humidity, &c., with 

 earth and atmosphere in a more intense state of chemical flux, 

 the synthesis of protoplasm took place. As the earth cooled 

 it ceased to appreciably affect the temperature of the atmosphere, 

 and the latter finally came to be maintained by the sun's rays 

 some 290 C. warmer than space. Atmosphere and water clung 

 to the earth owing to the attraction of gravity. The moon 

 with its smaller mass has long lost both. 



The question has often been raised as to whether life exists 

 in any of the other planets. The survey of terrestrial life shows 

 a wide range in the scale of physical conditions under which 

 protoplasm is capable of living. Condors circle round the peaks 

 of the Andes miles high in realms of cold attenuated air, fishes 

 swim in the profound depths of the ocean where the water 

 pressure is equal to two tons to the sq. inch. Algae have been 

 found in hot springs living at a temperature of 55 C., and 

 Richet discovered the sulphur organisms of Luchon living in 

 water at 70 C. Dollinger, in -a period of four years, gradually 



196 



