Elements of natural philosophy (Volume 2-3) . ies of thebodies in whose ether the wraves exist, increase, while,on the contrary, the distances between the ethereal mole-cules may increase. It would be more consonant to the principles of in-duction, to adopt the law expressed by Equation (92),which is but the simple consequence of known physi-cal principles, and conclude from the non-appearance ofcolor at the occupation of a star, that the distances be-tween the ethereal molecules which occupy the celestialregions are insignificant in comparison to the wavelengths. This would bring the final wa
Elements of natural philosophy (Volume 2-3) . ies of thebodies in whose ether the wraves exist, increase, while,on the contrary, the distances between the ethereal mole-cules may increase. It would be more consonant to the principles of in-duction, to adopt the law expressed by Equation (92),which is but the simple consequence of known physi-cal principles, and conclude from the non-appearance ofcolor at the occupation of a star, that the distances be-tween the ethereal molecules which occupy the celestialregions are insignificant in comparison to the wavelengths. This would bring the final waves at disappear-ance, of whatever length, all to the spectator at theAna appearances game ^g^^ . aiK] the same being true of the first waves thus accounted for. at reappearance, there should be no color. Conclusiondrawn fromknownprinciples; CHROMATIC ABERRATION. Chromaticaberration ; Illustration; §118. It fol-lows from the un-equal refragibili-ty of the elementsof white light,that the action ofa lens will be, toseparate these el- Fis. ELEMENTS OF OPTICS. 393 ernents and direct them to different foci, since the value Elements ofof/, in Equation (27), depends upon that of m. Sub-^t2to ..... iii ,. 1 •» / \. -. different foci; stituting in that equation — for _], m the case p \r v 1 of a spherical lens ; and writing fv and f„ for the focal distances of the violet and red rays, we obtain Relation between = (to0 - i) . —^- /. p / = ipir-i) — + —- the conjugatefocal distancesfor red andviolet; /, r p / in which ray, being greater than mr, fv, will be less than/r, and the violet rays will be brought to a focus departure from accurate convergence, caused by theunequal refrangibility of the elements of white light, when Chromaticdeviated by a lens, is called chromatic aberration, and aberrationdepends upon the nature of the lens and not on its e ne ;figure. It is measured, along the axis of the lens, by the its of fr - /„. The intersectio
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