XXIV. — Observations relatice to the Structure and Origin of the 



Diamond. 



By Sib DAVID BREWSTER, KG H. LL.D. F.R.S. &c. 



[Read February 27, 1833.] 



JLN the year 1820 I communicated to the Royal Society of Edinburgh an 

 account of a very singular fact relative to the structure of the diamond, and I 

 added to this communication some conjectures respecting- the origin of this 

 remarkable gem. As these conjectures have been referred to by some late 

 and able writers on the diamond mines of India without sufficiently separating 

 the fact from the conjectures, and as I consider the structure which 1 disco- 

 vered around the cavities in this mineral as a leading fact in the natural 

 history of this gem, I have been induced to re-examine it with care, and to 

 make a drawing of the phsenomena which it presents. 



In order to bring all the facts into one view, I shall make no apology for 

 quoting my original observations. 



"Had the diamond not been placed at the head of the mineral kingdom, 

 from its unrivalled lustre and high value as an ornamental gem, it would have 

 attained the same distinction from its great utility in the arts. Separated from 

 all other gems by its remarkable refractive power, and from all mineral sub- 

 stances by its extreme hardness, its chemical composition, and its locality in 

 the crust of the earth, it has always been regarded as an anomalous substance 

 which set even speculation at defiance. 



"When Sir Isaac Newton compared the refractive power of several bodies, 

 he remarked that amber and the diamond had a refractive power three times 

 greater in respect of their densities than several other substances, and he 

 conjectured that the diamond was probably an unctuous substance coagulated. 

 This relation between the inflammability of bodies and their absolute refrac- 

 tive power I had an opportunity of confirming and extending by ascertaining 

 that sulphur and phosphorus exceed even the diamond in absolute refractive 

 power, and that these three simple inflammable bodies stood at the head of all 

 other solid and fluid substances in their absolute action upon light. 



"In this arrangement, amber stood next to diamond ; and as both these sub- 



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