184 Prof. Challis on the Hydrodynamical Theory of the 



and its magnetic action being supposed to be attributable to 

 the setherial streams which, as indicated above, this state ge- 

 nerates when the substance is traversed either by steady streams 

 or a uniform series of vibrations, we have next to inquire re- 

 specting the origination of these primary movements of the 

 aether. I thought, at first, they might be due to the sethe- 

 rial streams which relatively pass through atomically constituted 

 substances in consequence of the earth's revolution about its 

 axis and motion in its orbit, and of the motion of the solar 

 system in space. But since in that case the primary, and by 

 consequence the secondary, motions would be subject to large 

 fluctuations of intensity to which there is nothing corresponding 

 in the phenomena of a magnet, it follows that the streams which 

 are the exponents of magnetism cannot be to any sensible 

 amount due to the above-mentioned primaries, and must have 

 a different origin. 



9. Having proved, as stated in art. 7> that the secondary 

 streams might be generated by a uniform series of setherial un- 

 dulations, and having repeatedly maintained (in articles in the 

 Philosophical Magazine and in my work on the Principles of 

 Physics) that attractions and repulsions may be attributed to 

 the dynamical action of such undulations on the individual 

 atoms of bodies, it occurred to me that those vibratory motions 

 of the sether which by their attractive effect maintain the regular 

 gradation of density might be the primaries sought for; and 

 this supposition is in accordance with the fact already adverted 

 to, that magnetism pertains to the magnetized body apart from 

 any extraneous action. [See^ respecting "Attraction by Vibra- 

 tions of the Air/' an article in the Philosophical Magazine for 

 April 1871. I cannot but regard the results of Mr. Guthrie's 

 experiments as singularly confirmatory of my theoretical anti- 

 cipations.] According to the views I have advocated relative to 

 molecular forces, the maximum velocity of the attractive vibra- 

 tions would be so much larger than that of the repulsive vibra- 

 tions, that in the present inquiry the latter may be left out of 

 account. Also it may be presumed that it is because that 

 maximum velocity very much exceeds the rotatory^ orbital, and 

 translatory motions of the earth, that these motions have com- 

 paratively no magnetic effect. 



10. Consequently, if, for simplicity, the magnet be supposed 

 to be of a cylindrical form, in its interior an impulsive action 

 upon the sether is continually operating in the directions parallel 

 to its axis. Now as the attractive action of a series of undula- 

 tions is in the direction contrary to that of propagation, and the 

 attraction is towards the denser end of the magnet, it follows 

 that the direction of the propagation, which is that of the maxi- 



