. The microscope and its revelations. denser than air, it will be bent to R. that istowards N. The whole course of the ray will be I C R, of whichthe part I C is called the incident r</?/. and C R the refracted I bambi i Mathematical Tab/< ;. THE LAW OF SINES 3 The angle I C makes with the normal X X7. viz. ION, is called theangle of incidence ; ;nid the angle R C makes with the normal X X,viz. R C X, is called the angle of refraction. Conversely, if a ray R C, travelling in water, meet the surface ofair A B in the point C, it will not continue in a straight line, butwill be bent t
. The microscope and its revelations. denser than air, it will be bent to R. that istowards N. The whole course of the ray will be I C R, of whichthe part I C is called the incident r</?/. and C R the refracted I bambi i Mathematical Tab/< ;. THE LAW OF SINES 3 The angle I C makes with the normal X X7. viz. ION, is called theangle of incidence ; ;nid the angle R C makes with the normal X X,viz. R C X, is called the angle of refraction. Conversely, if a ray R C, travelling in water, meet the surface ofair A B in the point C, it will not continue in a straight line, butwill be bent to the point I farther away from X-. Thus, when aray passes from a rarer to a denser medium it is bent or refractedtowards the normal, and when it passes out of a dense medium intoa rarer one it is bent or refracted airay from the normal. Further, if the shaded portion of the fig-ure were glass instead ofwater, the refracted ray RC would be bent still nearer X. and,conversely, if the ray passed out of glass into air, it would be more. FIG. 1.—The refraction of light. The Law of sines. 1tiit away from the normal than if it had passed out of water intoair. The angle of incidence ICX is connected with the angle of re-fraction RCX (as stated above) by what is known as Snells Law ofSines. The constant relation between the two sines for two specificmedia is called the refractive index of the medium, and is usuallyindicated in problems by the symbol ^. This law, stated with reference to the figure, would be : sine ICX = u — the refractive index or water,sine R C X In I C take any point, P, and from P draw P T perpendicularto NX. Similarly in RC take any point, F. and draw FH per-pendicular to X X. B 2 4 ELEMENTARY PRINCIPLES OF MICROSCOPICAL OPTICS Now, as sine I C N = I Land sine RCN = FHi, then, by PC F C PT Snells law, r= A*. FC As any points may be taken in T 0 and R C if the points had beenmore judiciously selected, we might have greatly .simplified the aboveexpression. Thus,
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