



E. B. Hunt on the Dispersion of Light. 373 



So unlimited and universal have I found its explanatory powers, 

 that it is hard to resist the conviction of its being a physical 

 verity. But wider still must its sphere of contact with nature 

 be pushed, before it can be unhesitatingly pronounced, a fact. 

 Yet has it already, for my mind, poured over nature so copious a 

 flood of light, and revealed in the universe so profound a design, 

 so sublime a system of legislation, sq beneficent a group of most 

 beautiful adaptations, that I have lost the power of neutrality and 

 cannotfbut wish its truth. A single detached inference from a 

 long connected series, is here presented in the following views 

 of refraction and dispersion; views, which without the aid of 

 the above law could scarcely have crossed my thought. 



Any wave in an elastic medium, must have a portion of its 

 mass denser than the surrounding medium. Consequently when 

 the particles or molecules of this fluid have assumed a mutual 

 equilibrium under the action of any local incessant force of at- 

 traction, the waves themselves must be attracted. In air at rest 

 under terrestrial gravitation, a sonorous wave suddenly propa- 

 gated, having a portion necessarily denser than the surrounding 

 medium, is like a heavy floating body at each successive instant 

 of time, and should therefore fall below a rectilinear course, m 

 its actual trajectory of propagation. Suppose such a pulse dis- 

 charged from the bore of a cannon and like ether pulses to be 

 propagated only along its rectilinear course : it would describe a 

 very flat projectile curve, by falling below the bore prolonged. 

 I The excess of density of the pulse only would cause this falling, 



for the air is buoyant — the amount of this excess divided by the 

 Glass of the pulse, would determine the distance fallen through 

 in any time. This ratio would enter, in comparing the heights fal- 

 len through by different pulses. The constant change of parti- 

 cles in the pulse would not affect the result, for the action and 

 composition of emanative force is instantaneous and incessant. 

 Refraction, 1 explain in a similar mode. The chief portion of 

 the space in ordinary bodies is occupied by molecular ether, 

 whose density in axial molecules based on axial atoms, and com- 

 posing axial crystals, is along the dividing surfaces and through 

 the interspaces, primarily dependent on the atomic axes, and sec- 

 ondarily on the molecular and crystalline axes. Take a medium 

 in molecular equilibrium; any wave in the surrounding ethereal 

 medium is attracted towards it like a buoyed heavy body; and 

 though the particles of the wave are constantly shifting, all im- 

 pressed attractions will be instantly and continuously combined 

 with the wave impulse and so transmitted. A pulse prop *ated 

 alono- a line will thus be deflected whenever the resultant of lat- 

 eral attractions is inclined to its course as in the case of oblique 

 incidence. This pulse being in a buoyant medium, it is only the 

 action due to its excess of density over surrounding ether which 



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