410 Mr, Herapath on the Causes, Laws, and principal [June, 



what we find by experience. Though regarded mathematically 

 such an inference would be strictly true, yet since the difference 

 between the forces will depend on the activity of the medium, 

 and since this activity wdl be increased in proportion to the 

 tenuity of the parts of the medium, it is evident that the ethereal 

 atoms may be so spaall, and the activity of the medium conse- 

 quently so great, that the swiftest motions we know of could 

 produce no sensible difference in the vigour of its action. For 

 instance, suppose one of the ethereal atoms to have the same 

 ratio to a particle of light, that a ball, a foot diameter, has to the 

 whole earth (and there is certainly nothing which forbids us to 

 suppose that the ratio might not be as little or even much less), 

 then caUing the earth 42000000 feet diameter, a thousand of 

 these ethereal atoms would individually, with the same force 

 that gives motion to a particle of light, receive a velocity more 

 than 74000000000000000000 times greater than that of hght. 

 But with such an activity, the law of attraction on a body mov- 

 ing with the velocity of light, in the direction of the attraction, 



54 



would not be augmented more than a th 



a.tt^ixiti.uc^ ixxuic tixaii 1000000000000000000000 



part of unity. And with this increase in the law of attraction. 

 It would be 2857796067672610 years before the apses of the 

 earth's orbit would move one second of a degree. But since 

 our calculation is made on the supposition theit the body with- 

 draws itself, as it were, from the action of the impelling power 



bwith the rapidity of light, the augmentation or diminution of the 

 law on a body, moving like any of the bodies of our planetary 

 system, would be many million times less ; and, therefore, it 

 would take many million times the period that I have assigned 

 to produce, with a fluid of such activity, a difference of V in the 

 position of the earth's apses. We may hence fairly conclude, 

 that there might be a fluid medium pervading the heavens and 

 all bodies of such activity, that no sensible difterence could be 

 observed in the intensity of its action on bodies in a state of 

 quiescence, or moving with a velocity, not only six milhon,* 

 but several million million times greater than that of hght. 



With the same views it would be easy to show that the resist- 

 ance which such an ethereal fluid would cause to the motions of 

 any of the celestial bodies, could produce no sensible effects in a 

 period of many million years. No objection, theretbre, so far as 

 it respects resistance or irregularity of law of action, can be made 

 to filling the heavens with a fluid of this kind, which it would 

 not be easy to answer ; and we might consequently infer, that 

 whatever has been demonstrated of an unresisting and a per- 

 meating gravitation, might be easily transferred to our fluid 



ijnedium. 



T N V J . 



' ' These things being granted, it follows, that since — is the 



♦ M. Upboe** System of the World, vol. ii. p. 2S4, by Mr. Pond, AR. 



