INFRA- WORLD MECHANICS AND PHYSICS 37 



This argument applies so long as the forces in- 

 volved are all purely mechanical. But it breaks 

 down as soon as gravitational, molecular, or electric 

 forces are brought into play. A mere increase of 

 velocity does not increase gravitation. If the 

 velocity of the earth increases ten times, the centri- 

 fugal force increases a hundred times, and unless 

 gravitational force increases to the same extent, 

 the earth will fly off into space. 



We do not know what constitutes gravitational 

 force. We only have an imperfect equation for it, 



\rxci 



viz., F = -pj r where F is the attraction, MM 1 are the 



masses, and D the distance. 



Gravitation is not the only force in want of a 

 mechanical interpretation. All " actions at a dis- 

 tance" are in the same predicament. Coulomb's 

 laws of electric and magnetic attraction are im- 

 perfect in their dimensions, and elasticity, cohesion, 

 capillarity, and molecular forces generally depend 

 upon actions which wo are as yet to a great extent 

 miliar with. 



If the pace of the world is accelerated, and the 

 world is still to go on as before, all forces, mechanical, 

 gravitational, electric, and molecular, must be in- 

 creased in the same proportion viz., as the square 

 . 



Matters are a little more complicated when not 

 only one, but all, quantities are altered simultane- 



