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That out of it one would be able to fashion pyramids, having their base square, pentagonal, hexagonal, or with as many sides as one desired, all the surfaces of which should have the same refractions as the natural surfaces of the crystal, except the base, which will not refract the perpendicular ray.
He could not well fail to know that different mediums refract light differently, and that for the same medium the amount of light valies with the change in the angle of incidence. He was not able, however, to generalize his observations as he desired, and to the last the law that governs refraction escaped him.
That night, long after dark, with twenty-five miles behind them, Linday and Tom Daw went into camp. It was a simple but adequate affair: a fire built in the snow; alongside, their sleeping-furs spread in a single bed on a mat of spruce boughs; behind the bed an oblong of canvas stretched to refract the heat. Daw fed the dogs and chopped ice and firewood.
They longed to dream under the perfumed snow of the interminable orange groves; to be masters of the sheltered valleys where the myrtle and the jasmine spice the salty air; where the aloe and the cactus grow between the stones of extinct volcanoes; where the mountains of marble extend their white veins down even into the depths of the sea and refract the African heat emitted by the opposite coast.
The action of the lens is aided by several refractive media in the eye. These media are the cornea, the aqueous humor, and the vitreous humor. By reason of their shape and density these media refract the rays of light, and bring them to a focus upon the retina, thus aiding in producing a sharp and distinct image of the object.
The strata of air, unequally heated, and therefore differing in rarity, refract the rays of light, fantastically enlarging and distorting the objects seen through them, which frequently appear raised from the ground and hanging in mid-air, or else, by a repetition of their image, which is reflected in a lower stratum, give the impression that they stand up out of a lake.
The apparatus consists of a central powerful lamp; round this is placed an arrangement of glass, so formed as to refract these beams into parallel rays in the required directions. Lenses were employed in lighthouses at a very early period. When they were first made they were used for burning instruments, by collecting the rays of the sun.
In so far as the dust-particles were opaque they would obscure these rays; where they were transparent or polished they would refract and reflect them. That the material of which those dust-particles was composed was very various has been ascertained, proved, and recorded by the Krakatoa Committee.
Fascinated by his talk, which seemed to play like lightning round a cliff at midnight, revealing not only measureless heights and soundless depths, but the greasy wrappings and refuse bottles of a picnic, the listener had an intuition that Heine's mind did indeed, as he claimed, reflect or rather refract the All.
But if the snowfall is very slight, the moisture content of the lower air sometimes is not exhausted before it stops; those large crystals remain at the surface and are not buried out of sight by the later fall. These large, coarse, slablike crystals reflect as well as refract the light of the sun. There is not merely the sparkle and glitter, but also the colour play.
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