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XXIX. Observations relative to the Structure and Origin of 



the Diamond, By Sir David Brewster, K.G.H. LL.D. 



F.R.S. $c* 

 TN the year 1820 I communicated to the Royal Society of 

 •ft Edinburgh an account of a very singular fact relative to 

 the structure of the diamond, and I added to this communica- 

 tion 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 suffi- 

 ciently separating the fact from the conjectures, and as I con- 

 sider the structure which I discovered 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 phenomena 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 mi- 

 neral 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 

 substances 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 specula- 

 tion 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 coagu- 

 lated. This relation between the inflammability of bodies and 

 their absolute refractive power I had an opportunity of con- 

 firming and extending by ascertaining that sulphur and phos- 

 phorus 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 substances had a similar locality, and had also 

 carbon for their base, it became of some importance to dis- 

 cover that their general polarizing structure was the same. 

 The analogy, however, to which I wish to direct the attention 

 of the Society is founded on the existence of small portions of 



* From the Transactions of the Geological Society, N.S., vol. iii. 

 p. 455. See Lond. and Edinb. Phil. Mug., vol. iii. p. 220. 



