VITALITY. 377 
muscles of mau 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 
