374 E. B. Hunt on the Dispersion of Light 



will deflect it. This excess and consequent deflection, being de- 

 pendent on the nature of the wave, should vary with the color 

 of the ray in light. This excess divided by the entire pulse and 

 multiplied by a particular function depending on the time of ac- 

 tion and intensity of the deflecting resultant, would measure the 

 refraction. The physical elements entering are, the intensity of 

 atomic attraction for the medium, and of repulsion between par- 

 ticles : the atomic radius on which the sphere of efficient action 



a* 





Jwe the time function ; and the specific densities of the incident 

 waves, on the differences between which dispersion depends. 

 The atomic or molecular attraction expressed in a series, after 

 reaching a moderate number of terms, each counting one molec- 

 ular diameter, becomes relatively very small, and the remainder 

 of the series may be neglected in its summation — that is, mo- 

 lecular attraction becomes evanescent before reaching a sensi- 

 ble distance ; its curve having both of the co-ordinate axes as 

 asymptotes, when one is an axis of distance and the other of 

 force. This is true if we even take the molecular diameter as 

 great as the limit which observation shows it cannot actually ex- 

 ceed. A ray pulse then, obliquely incident, is attracted sensibly 

 when it reaches an insensible distance from the refracting medi- 

 um, and the more so as the pulses become specifically denser. 

 The law of refraction and the values of the refractive index re- 

 sult as in the heterogeneous emission theory of Newton. The 

 irrationality of dispersive refraction would follow an inequality 

 between the atomic constants of media. The connection be- 

 tween density and refraction at once appears, and the chemico-me- 

 chanical peculiarities of oxygen even furnish a glimpse of the 

 cause of the high refractive indices of inflammable media. 



Whatever be the particular character of ethereal waves, they 

 must, under the law, be subject to atomic attraction. To enter 

 into an analysis of their mechanical peculiarities, is not here es- 

 sential, nor have I the mathematical attainment, so difficult a 

 subject demands. This would of course include heat waves, 

 waves of chemical action or any others which exist ; all of which 

 having a specific excess of density must undergo attraction. The 

 transversal vibration of luminous rays, is abundantly proved, and 

 neither seems to touch or be touched by what has preceded. 

 The difference between colored rays is in their amplitude of im- 

 dulation, the violet or rather the lavender being shortest, and the 

 red being longest; the former must be specifically densest, as 



being most refracted — the fa iting rays being still denser. 



The ideas here so imperfectly sketched, combine, as is obvious, 

 some points of the Newtonian and wave theories of light. -As- 

 signing to light the same mechanical nature as the latter, the rea- 

 son of refractive deviation is derived essentially from the former. 



