. The Family tutor . Fisr. 4. falls perpendicularly on any transparent oruncrystallized surface, as glass or water, it is partly reflected, partly scattered inall directions (which part renders theobject visible), and partly transmitted inthe same direction from which it comes.If, however, the light come in any otherthan a perpendicular or vertical direction,as from R to A, on the surface of a thickslip of glass, as represented in Fig. 4,it will not pass the glass in the line R A B,but will be bent or refracted at A to C.As it leaves the glass at C, it again travelsin a direction parallel to R
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. The Family tutor . Fisr. 4. falls perpendicularly on any transparent oruncrystallized surface, as glass or water, it is partly reflected, partly scattered inall directions (which part renders theobject visible), and partly transmitted inthe same direction from which it comes.If, however, the light come in any otherthan a perpendicular or vertical direction, as from R to A, on the surface of a thickslip of glass, as represented in Fig. 4, it will not pass the glass in the line R A B, but will be bent or refracted at A to C.As it leaves the glass at C, it again travelsin a direction parallel to R A, its firstcourse, llefraction, then, is the change cfdirection ivhich a ray of light snffers on pass-ing from a rarer to a denser medium, and thereverse. In passing from a rarer to adenser mediinn (as from air to glass orwater), the ray is bent or refracted towardsa line perpendicular to that point of thesurfiice on which the light falls, and froma denser to a rarer medium the law isreversed.. A common experiment, in illustrationof this law, is to place a coin in thebottom of a bowl, so situated that theobserver caimot see the coin until water ispoured into the vessel; the coin thenbecomes visible, because the ray of lightpassing out of tlie water from the coin, isbent towards the eye. In the same man-ner, a straight stick or spoon thrust intowater, appears bent at an angle where itenters the water. Jinount of Refraction.—The obliquityof the ray to the refracting mediumdetermines the amount of refraction. Themore obliquely the ray falls on the sur-face the greater the amount of refraction.A little modification of the last figure wi>lmake this clear. Let R A be a beam oflight falling on a refracting medium, it is CHEMISTllY. 7o bent as before to P/. If we draw a circleabout A as a centre, and a line a a, fromthe point a where tlie circle cuts the ray11 at right angles, to the perpendicularpassing through A, the line a a is calledthe siiie of the angle of incUleiice ; wh