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Sec. II, Ch. 1: The Diamond

Sec. II, Ch. 1: The Diamond Page of 366 Sec. II, Ch. 1: The Diamond Text size:minus plus Restore normal size   Mail page  Print this page
The Diamond.                                 57
Now, Newton found that the index of refraction of Dia­mond was much higher than he should have anticipated from the specific gravity of the stone. But he had observed that fatty and resinous bodies—such as oils, turpentine, and amber—possessed in like manner a higher refractive index than their density would suggest. Hence he was led to throw out the bold conjecture that the Diamond might be " an unctuous body coagulated ! "
Reflection and Dispersion.
In addition to its property of strong refraction, the Diamond possesses the power, in an extraordinary degree, of reflecting and dispersing the rays of light, thus causing what is technically termed the " play of colors," observ­able on a well-cut Diamond. The optical term " dispersion" is applied to the power which a transparent substance possesses of breaking up the incident white light into prismatic tints, like those of the rainbow—a power which is enjoyed to an unusual extent by the Diamond, and gives rise to the splendid flashes of fire emitted by a stone which has been skilfully cut.
As the value of a Diamond depends very materially · upon this play of colors, many methods have been essayed from time to time for testing it. Babinet recommended the following plan, which he himself was in the habit of employing, In a sheet of, white paper he pierced a hole somewhat larger than the Diamond to be tested ; he then let a ray of sun-light pass through the hole, and holding the Diamond a little distance from it, yet at such an angle as to allow the ray to alight on a point of a flat facet, he found this facet to be forthwith represented on the paper as a white figure, whilst all around little rainbow circles were delineated. If the observer found the primary colors,
Sec. II, Ch. 1: The Diamond Page of 366 Sec. II, Ch. 1: The Diamond
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