Ocular refraction and the shadow test . pear to be. Repeat experiment illustrated by figure 50, using a concave lensand no difference will be detected between the convex and concave;however, if experiment illustrated by figure 48 be made with a con-cave lens the results will be shown by figure 57. The lens beingmoved to the right, the portion of the line vS L seen through tne lens L E N S E S. 53 also appears to the right of the line S L or with the movement of thelens. A convex lens can be distins^nished from a concave, by the fact thatan object moves against the lens movement of a convex, an
Ocular refraction and the shadow test . pear to be. Repeat experiment illustrated by figure 50, using a concave lensand no difference will be detected between the convex and concave;however, if experiment illustrated by figure 48 be made with a con-cave lens the results will be shown by figure 57. The lens beingmoved to the right, the portion of the line vS L seen through tne lens L E N S E S. 53 also appears to the right of the line S L or with the movement of thelens. A convex lens can be distins^nished from a concave, by the fact thatan object moves against the lens movement of a convex, and loith the lensif it be concave. In the chapter on light it was explained that light was composedof rays of various wave length that gave the effect of color, a prismpossesses the power of separating white light into its component a band of light be admitted through a slit A figure 58, and trans-mitted by a prism P upon a screen S, it will be separated into aluminous band showing the colors of the spectrum, this is termed the. ppearanceof a vertical straight line tlirougli acoiua e spherica vision passing through the optical centre; III. lens moved to t displaced to the right. •ighl dispersion of light and is due to the difference of ihe degree ofdeviation of the various rays by refraction Red is deviated the leastand is said to be the least refrangible color, and in the order of re-frangibility come, orange, yellow, green, blue and violet, the violetbeing the most refrangible color. This creates in lenses what istermed chromatic aberration, the images fonned by strong sphericallenses are tinged with these colors. In figure 58 the spectrum color band is shown as having sevencolors, but it is merely a sub division of the blue into two shades,cyan blue an : ultramarine blue, according to a later idea of thespectrum. 54 OCULAR R L F R A C T I O N. Having found that various powers may be obtained in lenses,some method of numbering or indicating their power must necessar
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