THE FORCES OF THE INFRA-WORLD 1 7 



only one part in a billion of the " volume " of an 

 atom need be filled up by them. 



In view of the fact that the volumes of the sun 

 and all the planets put together fill up just about 

 one-billionth of the solar system within the orbit 

 of Neptune, the analogy between an atom and a 

 solar system becomes more strikingly evident. But 

 this part of the analogy is really implied in the 

 hypothesis that all lengths are reduced in the 

 same proportion. 



2. The superior density of the " celestial bodies " 

 of the infra-world implies that when they are set 

 in motion they have a billion times more kinetic 

 energy, volume for volume, than the planets of our 

 If, therefore, we were suddenly trans- 

 ported into the infra-world, we should know by 

 without any other indication, that circumstances 

 had changed. But we should soon find out other 

 and more fundamental ditVerences. The cosmic 

 velocities are, as we have seen, practically the same 

 in both worlds, both absolutely and as measured l>y 

 the standards of each world iinlei Mini* m ly. This is 

 due to the fact that a velocity is the ratio of a ap 

 to a time, or LT~ ! . If both L and T arc changed in 

 the same ratio, the result remains the same, and it 

 remains the same, too, when the unit is changed 

 to the same extent in both L and T. Hut an 

 acceleration is a length ii\ i.i.-d by the square of 



me, and if the units of both space ami time are 



B 



