VITALITY. 377 



muscles of man and animals, as much as that which we 

 develop by the combustion of coal or wood, has been pro- 

 duced at the sun's expense. The sun is so much the 

 colder that we may have our fires; he is also so much the 

 colder that we may have our horse-racing and Alpine 

 climbing. It is, for example, certain that the sun has 

 been chilled to an extent capable of being accurately 

 expressed in numbers, in order to furnish the power which 

 lifted this year a certain number of tourists from the vale 

 of Chamouni to the summit of Mont Blanc. 



To most minds, however, the energy of light and heat 

 presents itself as a thing totally distinct from ordinary 

 mechanical energy. Either of them can nevertheless be 

 derived from the other. Wood can be raised by friction 

 to the temperature of ignition; while by properly striking 

 a piece of iron a skillful blacksmith can cause it to glow. 

 Thus, by the rude agency of his hammer, he generates 

 light and heat. This action, if carried far enough, would 

 produce the light and heat of the sun. In fact, the sun's 

 light and heat have actually been referred to the fall of 

 meteoric matter upon his surface; and whether the sun is 

 thus supported or not, it is perfectly certain that he might 

 be thus supported. Whether, moreover, the whilom 

 molten condition of our planet was, as supposed by eminent 

 men, due to the collision of cosmic masses or not, it is per- 

 fectly certain that the molten condition might be thus 

 brought about. If, then, solar light and heat can be pro- 

 duced by the impact of dead matter, and if from the light and 

 heat thus produced we can derive the energies which we have 

 been accustomed to call vital, it indubitably follows that 

 vital energy may have a proximately mechanical origin. 



In what sense, then, is the sun to be regarded as the 

 origin of the energy derivable from plants and animals? 

 Let us try to give an intelligible answer to this question. 

 Water may be raised from the sea-level to a high elevation, 

 and then permitted to descend. In descending it may be 

 made to assume various forms to fall in cascades, to spurt 

 in fountains, to boil in eddies, or to flow tranquilly along 

 a uniform bed. It may, moreover, be caused to set com- 

 plex machinery in motion, to turn millstones, throw shut- 

 tles, work saws and hammers, and drive piles. But every 

 form of power here indicated would be derived from the 

 original power expended in raising the water to the height 



