ON THE INTERACTION OF NATURAL FORCES. 191 



In opposition to this it has been urged, that here in 

 Prussia the German knights in former times cultivated 

 the vine, cellared their own wine and drank it, which is 

 no longer possible. From this the conclusion has been 

 drawn, that the heat of our climate has diminished since 

 the time referred to. Against this, however. Dove has 

 cited the reports of ancient chroniclers, according to 

 which, in some peculiarly hot years, the Prussian grape 

 possessed somewhat less than its usual quantity of acid. 

 Tlie fact also speaks not so much for the climate of the 

 country as for the throats of the Grerman drinkers. 



But even though the force store of our planetary 

 system is so immensely great, that by the incessant 

 emission which has occurred during the period of human 

 histoiy it has not been sensibly diminished, even though 

 the length of the time which must flow by before a sen- 

 sible change in the state of our planetaiy system occurs 

 is totally incapable of measurement, still the 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 ? Men are in 

 the habit of measuring the greatness and the wisdom of 

 the universe by the duration and the profit which it pro- 

 mises to their own race ; but the past history of the earth 

 already shows what an insignificant moment th? duration 

 of the existence of our race upon it constitutes. A 

 Nineveh vessel, a Koman sword, awake in us the con- 

 ception 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 multi- 

 plied itself before the Pyramids or Nineveh could have 

 been erected. We estimate the duration of human his- 

 tory at 6,000 years ; but immeasurable as this time may 



