A
letter was lately published from Sir David Brewster, on a curious
optical phenomenon that had occurred in the construction of a diagonal
lens. The diamond, previous to working, had all the appearance of
internal brilliancy; but, after being polished, it presented a series
of stratified shades, which rendered it useless for the required
purpose. It afterwards appeared that lapidaries were acquainted with
this appearance, which rendered them extremely unwilling to take the
risk on themselves, of cutting up diamonds for optical purposes. On a
minute examination of this phenomenon, it appeared that these different
shades occurred in regular strata, each section being about the
one-hundredth part of an inch, and each stratum having a different
focus, and being of a different degree of hardness and specific
gravity. The inferences drawn from the above facts were :—that the
diamond was a vegetable substance, and that its parts must have been
held in solution and subjected to different degrees of pressure at
different stages of existence. If, on the contrary, as it has been
generally believed, it is subject to the laws of crystallization, its
crystals must necessarily be homogeneous.
