The Photographic art-journal . under the red glasssve obtained a negative image ; that is, all;ihe white parts of the engraving throughwhich the rays have passed will be repre-sented by ; and under the blueglass you will get an intense and positiveimageâ^-by bleaching out the brown colorof the paper under the white parts of theengraving. All these results go to prove,that from the lower end of the spectrumup to far beyond the extreme end of thevisible image, we have a considerableamount of chemical phenomena going on,but interrupted, and often obliterated, bythe influence of Light^
The Photographic art-journal . under the red glasssve obtained a negative image ; that is, all;ihe white parts of the engraving throughwhich the rays have passed will be repre-sented by ; and under the blueglass you will get an intense and positiveimageâ^-by bleaching out the brown colorof the paper under the white parts of theengraving. All these results go to prove,that from the lower end of the spectrumup to far beyond the extreme end of thevisible image, we have a considerableamount of chemical phenomena going on,but interrupted, and often obliterated, bythe influence of Light^ as manifested inthe colored rays. Now we find that theseprinciples do not obeyâwhich is the par-ticular point to which we have to directour attentionâthe same order of refrangi-bility in passing through any particularmedium. We discover, for example, tak-ing an ordinary single lens, that the resultof passing a sunbeam through such a lensis what 1 have endeavored to represent infig. 1. The actinic focus, A, falls nearer. the glass than the luminous focus, L, whichis still nearer than the focus for heat, chromatic dispersion of the raysthrough a glass of this kind is shown by blackening its centre, and then taking adisc of paper and passing it along the lineof the rays; where the rays diverge at h,h\ we shall find the paper will be fringedwith violet, and nearer the lens, as at r, r\the fringe will become red. We shall alsofind in such a case as this, that if we wereto place a piece of prepared paper at theend of that part which is marked as actin-ism, A, there the chemical effect wouldtake place in a very much shorter timethan at any other part between it and thebest luminous focus. Thus we get a lumi-nous image refracted to a certain extent;we obtain the calorific point, indicating amuch less refraction ; and we get the che-mical image refracted more considerably,â¢its focus thus falling nearer the inner sur-face of the lens. If we take a prism (), and s, *, *
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectphotogr, bookyear1851
