The Photographic art-journal . hich many ofour lenses are cemented. These examplesshow that the organic matter present inter-feres with the passage of those rays withwhich we particularly desire to work. Now, I need not go particularly into theconditions necessary to ensure the recom-bination of the particular rays produced bvrefraction. When we look through an or-dinary single lens, or a bad telescope, wefind all objects are fringed with color—wehave chromatic dispersion—and this arisesfrom the circumstance that every one ofthe colored rays has a distinct and separatefocal distance. Hence the
The Photographic art-journal . hich many ofour lenses are cemented. These examplesshow that the organic matter present inter-feres with the passage of those rays withwhich we particularly desire to work. Now, I need not go particularly into theconditions necessary to ensure the recom-bination of the particular rays produced bvrefraction. When we look through an or-dinary single lens, or a bad telescope, wefind all objects are fringed with color—wehave chromatic dispersion—and this arisesfrom the circumstance that every one ofthe colored rays has a distinct and separatefocal distance. Hence the object of a com-bination of lenses is to bring the coloredrays to one point, where they are reunitedinto white light. If we bring the face ofone prism up against the face of another,we recombine those prismatic rays whichwould be produced by refraction in onedirection, and obtain a spot of white lightby such recombination. I have endeavoredto show in the accompanying figure, some-thing like the result that takes place. We. start with a colored image whose parallelrays fall upon a lens of flint glass, that lensrepresenting virtually two prisms placedwith two of their faces together. Suppos-ing we use a double convex lens, repre-senting the conditions of two prisms placed 286 The Photographic Art-Journal. May, edge to edge, we should virtually produceachromaticity. The result of the singlelens of flint glass, aa, tig. 1, would be, as1 have endeavored to indicate;—the lumi-nous focus for flint glass, falling at thepoint (b). But by bringing against thisanother lens, see fig 3, which has a differ-ent refracting angle, or which varies in dis-persive power, (as, for example, a lens of?crown glass), the imaginary prisms beingplaced in opposite directions, as shown inthe figure, the result will be, that since therays are again bent in the opposite directionto that which they were traversing, thewhole of the colored rays fall upon thesame plane and produce white light. In this wa
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectphotogr, bookyear1851
