PROOF OF EXISTENCE OF A SUPRA-WORLD 1 1 7 



more of the heavenly vault. A body brought within 

 5000 light-years would be four times as effective as 

 before. So we may safely say that, given a dis- 

 tribution of stars as supposed, both luminous and 

 dark, our vision would be absolutely blocked at the 

 actual limit of the galaxy. 



NOTE B. 



The energy possessed by a body of m grammes 

 flying with a velocity of v cm. per second is 

 equal to $mv 2 ergs. If we, therefore, measure 

 the velocity of the gramme falling towards the 

 sun at any particular instant, we know its 

 energy of motion in other words, the amount of 

 energy it has acquired under the sun's attraction 

 since it started from infinite space. The amount 

 of this energy is, of course, quite definite and 

 measurable for any point in space, and is called 

 the "gravitational potential" due to the sun at 

 that point. The gravitational potential due to 

 a body at any point is inversely proportional to 

 the distance of that point. 1 In figures, it is 



OM 



expressed by -^-, where M is the mass of the 



attracting body, D the distance of the point in 

 space, and G the "gravitational constant" which 

 fixes the numerical value of the potential for 

 the particular units adopted. When the mass is 

 expressed in grammes, und the distance in centi- 

 metres, G is 6-66 x 10~ B . Thus, at the distance of 



1 An elementary proof of this useful theorem Is given in Chapter 

 III. of my " Electron Theory," p. 45. 



