176 ON THE ORIGIN OF THE PLANETARY SYSTEM. 



sources of power of our steam engines, are remains of 

 primitive plants the ancient production of the sun's 

 rays. 



Need we wonder if, to our forefathers of the Aryan 

 race in India and Persia, the sun appeared as the fittest 

 symbol of the Deity ? They were right in regarding it 

 as the giver of all life as the ultimate source of almost 

 all that has happened on earth. 



But whence does the sun acquire this force? It 

 radiates forth a more intense light than can be attained 

 with any terrestrial means. It yields as much heat as 

 if 1,500 pounds of coal were burned every hour upon 

 each square foot of its surface. Of the heat which 

 thus issues from it, the small fraction which enters our 

 atmosphere furnishes a great mechanical force. Every 

 steam-engine teaches us that heat can produce such 

 force. The sun, in fact, drives on earth a kind of 

 steam-engine whose performances are far greater than 

 those of artificially constructed machines. The circu- 

 lation of water in the atmosphere raises, as has been 

 said, the water evaporated from the warm tropical 

 seas to the mountain heights ; it is, as it were, a water- 

 raising engine of the most magnificent kind, with 

 whose power no artificial machine can be even dis- 

 tantly compared. I have previously explained the 

 mechanical equivalent of heat. Calculated by that 

 standard, the work which the sun produces by its 



