THE BIGGEST DIAMONDS 23 



used to keep it covered to develop a brown or purple 

 tint. This, then, is the explanation of the results 

 obtained by the French observer with corundum, as 

 reported a few months ago. There was no "trans- 

 formation " of one substance into another, nor did he 

 himself suggest that there was. The radium rays 

 merely acted chemically on minute impurities present 

 in colourless or pale-coloured crystals, and so produced 

 colour as they do in diamonds or in glass. 



9. Diamonds 



His Majesty King Edward was presented with the 

 great Cullinan diamond from the Transvaal in November 

 1907. This diamond weighs one pound and one-third 

 (avoirdupois) more than 21 oz. I have placed a good 

 glass model of it in the Central Hall of the Natural 

 History Museum ; in the case with it is a glass model 

 of another big diamond, the " Excelsior," as now cut, 

 and also models of the " Pitt " diamond, in the rough 

 and in the cut condition. Diamonds lose enormously 

 in the process of cutting. The Excelsior, like the 

 Cullinan, is a Cape diamond of fine quality, and free 

 from colour. It was the biggest diamond known until 

 the giant Cullinan was found : in the rough it weighed 

 7 07., or less than a third of the Cullinan. As now cut, 

 it only weighs 1} oz. It is reduced to a quarter of its 

 original size. 



In the same way, the Pitt diamond, an Indian one, 

 named after General Pitt, of Madras, weighed originally 

 3 oz., and is now (it is in Paris, in the Louvre, and is 

 called " The Regent ") less than an ounce in weight. 

 The biggest Indian diamond known the Nizam is not 

 quite twice this size, whilst the Kohinoor, which is 

 probably a fragment (a third) of the " Great Mogul " 

 a diamond which has disappeared, leaving only tradition 



