46 FROM NEBULA TO NEBULA 



certain the degree of tension brought to bear on the 

 material of Neptune's alleged ring. Not to weary the 

 reader w T ith too much detail, let me give a few calculated 

 results. The attraction of the sun on a given particle 

 as distant from him as Neptune, is about one fourteen- 

 hundred-thousandth as great as that of our earth on a 

 like particle at her surface. It is only about one-fortieth 

 as great as that of the moon upon the ring on your 

 finger, and is proportionally about equivalent to that 

 of the attraction of your own body upon the clock rest- 

 ing on the mantel a few feet from you. 



Now, gravitational attraction is one thing, but fric- 

 tional propulsion by it is altogether another. It is quite 

 admissible to conceive of the particles of which we are 

 speaking as being held back by their mutual gravita- 

 tional attraction from escaping into outer space; but it 

 demands the maximum of credulity, scientific or other- 

 wise, to believe that the friction between particles so 

 sparse and minute as here demonstrated, and bound to 

 each other by a tie so slender, could ever, under any cir- 

 cumstances, sustain a general rotational motion. To 

 refer again to our illustration, this friction is relatively 

 the same as the act of turning around on your heels 

 (while still preserving the intervening distance) would 

 have on the clock, not to draw it toward you, remember, 

 but to rub it to one side no, even less, because the air 

 intervening between the clock and you is ever so much 

 denser than the postulated nebula, and consequently 

 a stronger frictional medium. 



But perhaps I shall be told that I have mistaken 

 the principle governing this movement; that the prin- 

 ciple involved is really that of viscosity, or, if not that, 

 then the only other possible, namely, independent iner- 

 tial movement on the part of each particle. 



