170 ON THE INTERACTION OF NATURAL FORCES. 



inexorable laws of mechanics indicate that this store of force, 

 which can only suffer loss and not gain, must be finally exhausted. 

 Shall we terrify ourselves by this thought 1 Men are in the 

 habit of measuring the greatness and the wisdom of the universe 

 by the duration and the profit which it promises to their own 

 race ; but the past history of the earth already shows what an 

 insignificant moment the duration of the existence of our race 

 upon it constitutes. A Nineveh vessel, a Roman sword, awake 

 in us the conception of grey antiquity. What the museums of 

 Europe show us of the remains of Egypt and Assyria we gaze 

 upon with silent astonishment, and despair of being able to carry 

 our thoughts back to a period so remote. Still must the human 

 race have existed for ages, and multiplied itself before the 

 Pyramids or Nineveh could have been erected. We estimate 

 the duration of human history at 6,000 years ; but immeasur- 

 able as this time may appear to us, what is it in comparison with 

 the time during which the earth carried successive series of rank 

 plants and mighty animals, and no men ; during which in our 

 neighbourhood the amber-tree bloomed, and dropped its costly 

 gum on the earth and in the sea; when in Siberia, Europe, and 

 North America groves of tropical palms flourished; where 

 gigantic lizards, and after them elephants, whose mighty remains 

 we still find buried in the earth, found a home 1 Different 

 geologists, proceeding from different premises, have sought to 

 estimate the duration of the above-named creative period, and 

 vary from a million to nine million years. The time during 

 which the earth generated organic beings is again small when 

 compared with the ages during which the world was a ball of 

 fused rocks. For the duration of its cooling from 2,000 to 200 

 Centigrade the experiments of Bishop upon basalt show that 

 about 350 millions of years would be necessary. And with 

 regard to the time during which the first nebulous mass con- 

 densed into our planetary system, our most daring conjectures 

 must cease. The history of man, therefore, is but a short ripple 

 in the ocean of time. For a much longer series of years than 

 that during which he has already occupied this world, the exist- 

 ence of the present state of inorganic nature favourable to the 



