Fifth book of lessons for the use of schools . It is evident that convergent rays become more con-vergent with convex lenses, and divergent rays moredivergent with concave lenses. ^e shall next explain the refractions of a triangularpiece of glass ealled a prism. The sides are flat; it REFRACTION AND COLOURS. 343. cannot, therefore, bring the rays to afocus, nor can its refraction be similar tor- %? that of a flat pane of glass, because ithas not two sides parallel. The re-fractions of the light, on entering and on quitting theprism, are both in the same direction.* On enteringthe prism p, the
Fifth book of lessons for the use of schools . It is evident that convergent rays become more con-vergent with convex lenses, and divergent rays moredivergent with concave lenses. ^e shall next explain the refractions of a triangularpiece of glass ealled a prism. The sides are flat; it REFRACTION AND COLOURS. 343. cannot, therefore, bring the rays to afocus, nor can its refraction be similar tor- %? that of a flat pane of glass, because ithas not two sides parallel. The re-fractions of the light, on entering and on quitting theprism, are both in the same direction.* On enteringthe prism p, the ray is refracted from B to c, and onquitting it, from c to D. If the window-shutters beclosed, and a ray of light, admitted through a smallaperture, fall upon a prism, it will be refracted, and aspectrum, a b, representing all the colours of the rain-bow will be formed&v,;U. on the opposite is difficult to con-ceive how a piece ofwhite glass can pro-duce such a variety ofbrilliant colours; but the fact is, that the colours arenot formed by the prism, but existed in the rayprevious to its refraction; for the white rays of the sunare composed of coloured rays, which when blendedtogether, appear colourless or white. Sir Isaac Newton, to whom we are indebted for themost important discoveries res
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