292 ANNUAL OP SCIENTIFIC DISCOVERY, 



OBSERVATIONS ON THE DIAMOND. 



SIR DAVID BREWSTER at the Belfast meeting of the British Asso- 

 ciation stated that his opinion had been requested by Prince Albert 

 respecting different forms into which it was proposed to reduce 

 the Koh-i-noor diamond, in order to make it an ornamental 

 gem. In the state in which it then was, it exhibited an inferior dis- 

 play of colors to its glass model, and it was only by surrounding it 

 with a number of vivid lights that its colored refractions could be 

 developed. Having had occasion to observe some remarkable phe- 

 nomena in small portions of diamond, I was desirous of examining so 

 large a mass of diamond as the Koh-i-noor before it was reduced in 

 size, and covered with facets which would not permit it to be exam- 

 ined. His Royal Highness readily granted my request, and I had 

 thus an oppportunity of submitting it to the scrutiny of polarized 

 light. In place of producing no action upon this species of light, as 

 might have been expected from its octahedral structure, it exhibited 

 streaks of polarized tints, generally parallel to one another, but in 

 some places of an irregular form, and rising to the yellow of the first 

 order of colors. These tints and portions of polarized light were 

 exactly the same as those which I had long ago found in many other 

 diamonds. In placing the Koh-i-noor under a microscope of consid- 

 erable power, I observed in it, and also in each of the two small dia- 

 monds which accompanied it, several minute and irregular cavities, 

 surrounded with sectors of polarized light, which could only have been 

 produced by the expansive action of a compressed gas, or fluid, that 

 had existed in the cavities when the diamond was in a soft state. In 

 an external cavity, shown in the model, and which had been used for 

 fixing the gold setting, I observed, with common light, a portion of 

 yellow light, indicating a yellow substance. Mr. Garrard and others 

 considered it as gold rubbed off the gold setting ; but as gold is never 

 yellow by transmitted light, I considered the color as produced by a 

 yellow solid substance of unknown origin. Sir De la Beche having 

 suggested to me that it would be desirable to make a general examina- 

 tion of the principal diamonds in London, I went next day to the 

 British Museum, and found there an interesting specimen, which threw 

 some light on the yellow solid to which I have referred. This speci- 

 men was a piece of colorless diamond, uncut, and without any crys- 

 talline faces, about three or four tenths of an inch broad, and about 

 the twelfth of an inch thick, and on its surface there lay a crystal of 

 yellow diamond, with the four planes of semi-octahedron. This singu- 

 lar fact was illustrated by a large model placed beside it. Upon 

 examining the original, I noticed a pretty large cavity in the thickness 

 of the specimen, with the extremity of which the yellow octahedron 

 was connected ; and finding a portion of amorphous yellow diamond 

 in the other end of the cavity, I had no doubt that the yellow crystal 

 had emerged, in a fluid state, from the cavity when it was accidentally 

 opened, and had immediately crystallized on the surface of cleavage. 

 I am well aware that such an opinion makes a good demand upon the 



