J61 Prof. ChaWWs Explanations of Phenomena of Light 



propagation, although uniform, will he different. And even if 

 m should he the same for every primitive series of undulations, 

 its value might he altered (as there will he occasion to point out 

 hereafter) hy arbitrary conditions to which the undulations may 

 he subjected. It must therefore be admitted as a theoretical 

 result, that different undulations are propagated with uniform 

 velocities slightly different. The relative effect of this circum- 

 stance would be taken into account by supposing the quantity c 

 to vary slowly with the time. I am not aware that the explana- 

 tions of any phenomena of light would be thereby affected. 



Next, it may be remarked that as the expressions for the velo- 

 cities and condensation contain the constant factor m, and as the 

 dynamical effect of the pethereal undulations results from their 

 velocity and pressure, the amount of such effect must depend 

 upon the value of that factor, which may consequently be 

 regarded as the symbolical exponent of the quality of light 

 named its intensity. We shall hereafter have occasion to speak 

 of expressions for the amounts and variations of luminous inten- 

 sity ; at present a few preliminary remarks may be made rela- 

 tive to the circumstances under which the intensity is initially 

 determined. 



It must be concluded from experiment, as will be fully shown 

 in a subsequent part of this communication, that the sensation 

 of light is in no degree due to the velocity w, but depends ex- 

 clusively on the transverse velocity V. This must be accepted 

 as an experimental indication, which it does not belong to the 

 part of the undulatory theory of light now under consideration 

 to account for, the fact depending on dynamic relations between 

 the sether and the constituent atoms of the eye. In like man- 

 ner we must conclude from experiment that light is produced 

 by transverse movements of the sether within distances from the 

 axis very small compared to X, it being a known fact that spaces 

 very much narrower than the breadth of an undulation have been 

 made visible by powerful microscopes. This limitation, as we 

 have already seen, corresponds to an analytical circumstance, 

 which, however, does not of itself explain why the more distant 

 movements are inoperative in regard to light. The two limita- 

 tions being admitted, the analytical expression of the transverse 

 accelerative force which, by acting on the molecules of the eye, 

 excites the sensation of light, will be 



d?d<i Sm/car . 2tt . . . 



~ -jr-> or -^j- sin y- (ieat—z + c), 



the value of r being very small compared to \. Hence this force 

 for every separate ray varies as the distance from the axis. Con- 

 sequently for a bundle of rays the same law, as is known, would 



