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50 The Diamond.
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in
some instances light was slightly changed in passing through it, and
its power of refraction is enormous, and its dispersion comparatively
small, as a comparison with that of common glass will show:—
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To
these qualities are attributable its extraordinary brilliancy and play,
and it was the observation of these properties which led Newton to the
conclusion that it was a combustible body, and, later, caused several
scientific men to endeavour to apply it to optical and microscopical
purposes. It was, however, found by Sir David Brewster, that the
inequalities of its structure caused too much aberration of light to·
make it serviceable for these purposes.
It
is a non-conductor of electricity, and becomes positively electric by
friction ; but soon loses its power, namely, at the expiration of half
an hour.
The
diamond cuts glass with great facility, but not every stone can be used
for that purpose. It is required to find one whose angles are naturally
acute. These stones are called "glaziers," and fetch £10 the carat. Although most gems will scratch glass, it is only the diamond which is capable of cutting it.
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