236 KINETIC THEORIES OF GRAVITATION. 



reason should arise to think that the physical condition of the force par- 

 takes generally of the nature of a current or of a ray, a view which the 

 author inclines to, he sees no objection in the term." * 



" In the action of gravity, for instance, the line of force is a straight 

 line, -as far as we can test it by the resultant phenomena. It cannot be 

 deflected or even affected, in its course. Neither is the action in one line 

 at all influenced, either in direction or amount, by a like action in another 

 line."t This is the affirmation made by our first proposition. 



Faraday continues : " There is one question in relation to gravity, 

 which, if we could ascertain or touch it, would greatly enlighten us. It 

 is, whether gravitation requires time. If it did, it would show unde- 

 niably, that a physical agency existed in the course of the line of force. 

 It seems equally impossible to prove or disprove this point, since there 

 is no capability of suspending, changing, or annihilating the power, or 

 annihilating the matter in which the power resides." | Some six years 

 before the date of this latter paper. Professor Faraday, in "Thoughts on 

 Ray- vibrations," had suggested more doubtingly, the same inquiry : " I 

 am not aware whether there are any data by which it has been or could 

 be ascertained whether such a power as gravitation ects without occu- 

 pying time."§ 



This query finds its answer in our fourth proposition. The writer was 

 evidently not aware that it had been definitely settled by the astrono- 

 mers, and with a delicacy of precision infinitely beyond the reach of 

 any direct or instrumental' research ; and not being a mathematician, 

 he very naturally supposed the problem insoluble. Those not trained 

 in the higher operations of the science of " necessary conclusions," have 

 no conception of the resources of mathematical investigation applied to 

 judicious comparisons of accurate observations. And just here the 

 reminder may be permitted, that did the influence of gravitation occupy 

 .the millionth part of a second in traversing the distance of a million 

 miles, the astronomer's analysis would easily detect it. This would 

 represent only.one-ninth of the velocity estimated by Laplace and Arago, 

 as previously stated. 



* L. E. D., Phil. Mag., 1852, vol. iii, p. 67. Dr. P. M. Roget showed in 1831, by a very 

 neat geometrical demonstration, that these so-called " lines of force " in the magnetic 

 field, are simply the tangential resultants of the directive action by the two magnetic 

 poles exerted in straight or radial lines with a ratio of diminished intensity as the 

 square of the distance from either pole, on the minute iron particles regarded as 

 needles. (Journal of the Royal Institution, February, 1831, vol. 1, pp. 311-318; and 

 also a treatise on " Magnetism " by the same author, in vol. ii of the " Library of 

 Useful Knowledge," chap, ii, sect. 3, pp. 19-21.) M. Ch. Cellerier has also, by an 

 analytical discussion of the "magnetic curves," established the same conclusion 

 mathematically. (A Treatise on Electricity, by Aug. De La Rive, London, 2 vols., 8vo, 

 18.53. part iii, chap. i. Note D, vol. i, pp. 542-544.) 



t Phil. Mag., 18i2, vol. iii, p. 40.3. 



t Ibidem, p. 403. 



«J Phil. Mag., May, 1846, vol. xxviii, p. 349. 



