178 FROM NEBULA TO NEBULA 



the rigid hoop at a given number of revolutions per 

 minute, or, the elastic one? The deformation of the 

 latter cannot, of course, be effected without the absorp- 

 tion of power ; shall we then conclude that to rotate it at 

 the same rate of speed as the other will require just this 

 much additional power! Assuredly not! "But," you 

 may say, "then the act of deformation does not absorb 

 energy as at first supposed? How can we explain this 

 apparent paradox?" The answer is plain enough. That 

 part of the centrifugal force which in one case manifests 

 itself in elongating the elastic hoop, that is to say, causes 

 visible distortion, transforms itself into heat in the case 

 of the rigid one by forcing its molecules violently against 

 each other, from within outward. Let this pressure pass 

 a certain mark and we have the phenomenon of an explo- 

 sion, as, indeed, often occurs in the case of fly-wheels. 



These reflections bring out still another radical dis- 

 tinction between my views and those of Newton, namely, 

 that whereas he claims that, having once been given its 

 rotatory motion, no matter how, a planet will continue 

 to revolve forever from sheer inertia, I contend that the 

 earth, even if it were absolutely rigid and possessed a 

 mathematically spherical shape, would automatically 

 bring itself to axial rest by converting and yielding up its 

 centrifugal force into kinetic energy, or heat, and radiat- 

 ing the same out into space. There simply must be some 

 driving power behind the earth's rotation. What is it? 

 Is it natural or supernatural, mechanical or miraculous, 

 real or imaginary, physical or verbal, inertial or creative ? 

 Calling a fly-wheel persistent will not enable us to dis- 

 pense with the engine, nor will it serve any better for the 

 earth's case. 



The reader will doubtless remember that in estimat- 

 ing the energy of the earth 's attraction upon the moon I 

 adopted as a convenient, though perhaps somewhat 

 arbitrary, standard one horse-power as equivalent to the 

 sustentation of one ton, stationary, against gravity. This 

 is obviously an overestimate, but as it is an error on the 

 safe side, and as only approximate results will here be 



