Question: Show how the hypothenuse face of a right-angled prism may be used as a reflector. What connection is there between the refractive index of a medium and the angle at which an emergent ray is totally reflected?
Answer: Any face of any prism may be used as a reflector. The con nexion between the refractive index of a medium and the angle at which an emergent ray does not emerge but is totally reflected is remarkable and not generally known.

And from my pillow, looking forth by light
Of moon or favouring stars, I could behold
The antechapel where the statue stood
Of Newton with his prism and silent face,
The marble index of a mind for ever
Voyaging through strange seas of Thought, alone.

And if one look through a Prism upon a white Object encompassed with blackness or darkness, the reason of the Colours arising on the edges is much the same, as will appear to one that shall a little consider it. If a black Object be encompassed with a white one, the Colours which appear through the Prism are to be derived from the Light of the white one, spreading into the Regions of the black, and therefore they appear in a contrary order to that, when a white Object is surrounded with black. And the same is to be understood when an Object is viewed, whose parts are some of them less luminous than others. For in the borders of the more and less luminous Parts, Colours ought always by the same Principles to arise from the Excess of the Light of the more luminous, and to be of the same kind as if the darker parts were black, but yet to be more faint and dilute.

In 1808 … Malus chanced to look through a double refracting prism at the light of the setting sun, reflected from the windows of the Luxembourg Palace. In turning the prism round, he was surprised to find that the ordinary image disappeared at two opposite positions of the prism. He remarked that the reflected light behaved like light which had been polarized by passing through another prism.

The whole inherent pride of human nature revolts at the idea that the lord of the creation is to be treated like any other natural object. No sooner does the naturalist discover the resemblance of some higher mammals, such as the ape, to man, than there is a general outcry against the presumptuous audacity that ventures to touch man in his inmost sanctuary. The whole fraternity of philosophers, who have never seen monkeys except in zoological gardens, at once mount the high horse, and appeal to the mind, the soul, to reason, to consciousness, and to all the rest of the innate faculties of man, as they are refracted in their own philosophical prisms.

We have one of his [Newton’s] college memorandum-books, which is highly interesting. The following are some of the entries: “Drills, gravers, a hone, a hammer, and a mandril, 5s.;” “a magnet, 16s.;” “compasses, 2s.;” “glass bubbles, 4s.;” “at the tavern several other times, £1;” “spent on my cousin, 12s.;” “on other acquaintances, 10s.;” “Philosophical Intelligences, 9s. 6d.;” “lost at cards twice, 15s.;” “at the tavern twice, 3s. 6d.;” “to three prisms, £3;” “four ounces of putty, 1s. 4d.;” “Bacon’s Miscellanies, 1s. 6d.;” “a bible binding, 3s.;” “for oranges to my sister, 4s. 2d.;” “for aquafortis, sublimate, oyle pink, fine silver, antimony, vinegar, spirit of wine, white lead, salt of tartar, £2;” “Theatrum chemicum, £1 8s.”