THE ORGANISM AS A MECHANISM 55 



The energy of the solar system is in part the kin- 

 etic energy of those parts of it which are in motion — 

 planets, planetesimals, 1 and satellites. This quantity 

 of energy is enormously great. In the case of our earth 

 it is Imv 2 , m being the mass of the earth, and v its 

 velocity. Translated into numerical symbols we find 

 this quantity almost inconceivable. The greater part 

 of this energy is unavailable, that is, it can undergo no 

 transformations. But because the earth is in rotation 

 at the same time as it revolves round the sun, and 

 because the moon revolves round the earth, there are 

 tides in the watery and atmospheric envelopes of the 

 earth. The energy of the tides is the kinetic energy 

 of water or air in motion, and we can employ this 

 energy in the production of transformations, and it is 

 therefore available. But well-known investigations 

 have shown that the tides produce friction, and that 

 the period of rotation of the earth is slowly becoming 

 greater. Ultimately the earth will rotate on its own 

 axis in the same time that it revolves round the sun — 

 then a year and day will be of the same length. When 

 that occurs, the sun, earth, and moon will be in equi- 

 librium, and tidal phenomena due to the sun will cease. 

 The kinetic energy of the earth, rotating once in 24 

 hours is obviously greater than its kinetic energy when 

 rotating in the period which will then be its year. 

 What has become of the balance ? It has been 

 transformed into the mechanical friction of the tides 

 against the surface of the earth, 2 and this friction has 

 been transformed into low-temperature heat, and this 

 heat has been radiated off into space. 



1 Meteorites, cosmic dust, and other small particles moving in the solar 

 system within influence of the sun's gravity. 



2 Not entirely, of course, but whatever be the transformation it ends in 

 heat production. 



