Human physiology : designed for colleges and the higher classes in schools and for general reading . nt, I will call your attention to certain principles, whichwe shall find illustrated more beautifully and perfectly in theeye than in any optical instrument which man has ever con-structed. 432. The rays of light coming from any luminous point goin straight lines in all directions, just as the vibrations of sounddo, and, like them, become less intense the farther they arediffused. But they move in straight lines only so long as theyremain in the same medium. When they pass from one me-dium, int
Human physiology : designed for colleges and the higher classes in schools and for general reading . nt, I will call your attention to certain principles, whichwe shall find illustrated more beautifully and perfectly in theeye than in any optical instrument which man has ever con-structed. 432. The rays of light coming from any luminous point goin straight lines in all directions, just as the vibrations of sounddo, and, like them, become less intense the farther they arediffused. But they move in straight lines only so long as theyremain in the same medium. When they pass from one me-dium, into another they are bent out of their straight course,or refracted, as it is termed, unless they pass from one to theother in lines perpendicular to the surface of the medium which theyenter. This may be illustrated bythe following experiment. Placea coin, a, in the bottom of a basin,as represented in Fig. 156, and thenwithdraw from it so far that thecoin may be hidden from your eyeby the edge of the basin, as repre-sented in the figure. Keeping youreye fixed in that position, pour some FIG. 288 HUMAN PHYSIOLOGY. Refraction as light passes from a rarer into a denser medium, and vice versa. water into the basin up to the level, c. The coin will againbecome visible to your eye. The reason is, that the rays oflight, as they come from the water into the rarer medium, theair, are refracted or bent downwards, that is from the perpen-dicular. The effect of this may be seen in the figure. A rayof light, coming from the coin in the direction a, d, does notpass to d, but is bent downward, and so passes to the- eye ate. And so of other rays coming from the object. The coin,therefore, is seen by the eye at c, but it is not seen in its truedirection from the eye which is in the line e, c, a. The only pointin which the eye can see the coin in its true position is whenthe eye is at 6, in a perpendicular line directly over it. A raythat passes from one medium to another in a line perpendi
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Keywords: ., bookauthorhookerwo, bookcentury1800, bookdecade1850, bookyear1854
