152 



NATURE 



[April 7, 1910.,'^ 



procurable crystals for his investigations, and, if they 

 are artificial chemical preparations, if he has followed 

 and makes use of the recent work on the preparation 

 of perfect individual crystals, and the precautions to 

 be taken to avoid disturbance during growth, there 

 will be a very diiferent story to tell, and the deforma- 

 tions, striations, curvings, and lack of constancy of 

 ten minutes or more will all disappear, and the angles 

 will inform him, if he employs the most accurate 

 goniometer in the market, of their constancy to the 

 last minute. To speak, moreover, of "petites dimen- 

 sions " as being a drawback is even more enlightening 

 as to the author's lack of familiarity with practical 

 crystallography. For it is precisely small crystals, 

 varying from a very small pea to a pin's head in size, 

 that the crystallographer chooses by preference for his 

 measurements. For the liability to distortion is then 

 at its minimum. 



Sufficient will have been said to indicate the ex- 

 cellences and the defects of this volume, both striking 

 in their way. Indeed, in spite of the aggravating 

 defects which it has been essential to point out, the 

 writer possesses so original and lively a style, and his 

 remarks are often so well worth reading, that with all 

 its shortcomings, the book has good and valuable 

 qualities, and in the portions where the author is on 

 his own domain is both well written and instructive. 



A. E. H. TuTTOx. 



TEE ORIGIN OF THE DIAMOND. 

 Diamonds. By .Sir William Crookes, F.R.S. Pp. xvi 



+ 146. (London and New York: Harper and 



Brothers, 1909.) Price 2^. 6d. net. 

 A LL who have had the pleasure of hearing Sir 

 /^V William Crookes 's lectures on the diamond and 

 Its origin will be glad to find the valuable information 

 contained in them put into a permanent form in the 

 little book before us. 



The author has had exceptional opportunities for 

 studying the subject. During two visits to South 

 Africa, in 1896 and 1905, he was allowed by the 

 managers of the De Beers mines to have unrestricted 

 access to valuable sources of information ; and, as is 

 so well known, his own physical and chemical re- 

 searches have been largely concerned with questions 

 connected with the properties and origin of the most 

 remarkable, as well as the most highly prized, of 

 the gems. 



Concerning the Kimberley diamond mines, as well 

 as the alluvial deposits of South Africa, Sir William 

 Crookes can write with authority from his personal 

 observations. As illustrating "the kind of specula- 

 tive gambling " which goes on in the former class of 

 ■workings, we are told of a claim where the owner 

 had not seen a diamond for a fortnight, but just before 

 then he had picked out a diamond worth 300/. ! On 

 the other hand, the systematic work at the mines of 

 the De Beers Company enables the management to 

 regulate the annual supply with the greatest nicety, 

 so as not to cause any fall in the price of the gem. In 

 1907 more than two and a half million carats were 

 raised, which realised 6,452, 597Z. The mode of occur- 

 rence of the diamonds, the methods of working 

 NO. 21 10, VOL. 83] 



adopted at diflerent times in the wonderful pipes that 

 yield the gems, and the ingenious methods of treat- 

 ing the "blue ground" and sorting out the stones, 

 are described and illustrated by photographs taken by 

 the author himself. 



Sir William Crookes had the opportunity of hand- 

 ling and taking a photograph of the celebrated 

 " CuUinan diamond" before it was cut, and his de- 

 scription of it is of much interest. He tells us that : — 



"A beam of polarised light passed in any direction 

 through the stone, and then through an analyser, re- 

 vealed colours in all cases, appearing brightest when 

 the light passed along the greatest diameter— about 

 4 inches. Here the colours were very fine, but no 

 regular figure was to be seen. Round a small black 

 spot in the interior of the stone the colours were very 

 vivid, changing and rotating roiund the spot as the 

 analyser was turned. These observations indicated 

 internal strain. The clearness throughout was re- 

 markable, the stone being absolutely liquid like water, 

 with the exception of a few flaws, dark graphitic 

 spots, and coloured patches close to the outside. At 

 one part near the surface there was an internal crack, 

 showing well the colours of thin plates. At another 

 point there was a milky, opaque mass, of a brown 

 colour, with pieces of what looked like iron oxide. 

 There were four cleavage planes of great smoothness 

 and regularity. On other parts of the surface the 

 crystalline structure was very marked. The edges 

 were rounded in parts, and triangular markings 

 (depressions) were to be seen. I also noticed square 

 depressions, nearly as sharp and perfect as the tri- 

 angular ones." 



Interesting as this description undoubtedly is, we 

 cannot but regret that, before this unique specimen 

 was deprived of its interest for mineralogists by being 

 cut, no opportunity was afforded to the author, or any 

 other scientific investigator, of carrying out such a 

 series of observations in the laboratory as would have 

 enabled him to place on record all the facts about it 

 which it was desirable to obtain. 



A full account of the Canon Diablo meteorite, with 

 its enclosed diamonds, and of the vast crater-like 

 depression in Arizona where it was found, is given 

 in the concluding chapter. The author, in discussing 

 the genesis of diamonds, is clearly of opinion that, 

 whether of inter-terrestrial or of extra-terrestrial origin, 

 the conclusion is established, both by observation and 

 experiment, that the solvent from which the carbon 

 has crystallised must have been molten iron. 



In conclusion, we cannot but commend, to all de- 

 sirous of learning what is known about the most 

 beautiful and interesting of gems, this terse and 

 attractive — but withal trustworthy and complete — 

 summary of all the information on the subject which 

 has up to the present been acquired. J. W. J. 



DIFFERENTIAL GEOMETRY. 

 A Treatise on the Differential Geometry of Curves 

 and Surfaces. By Prof. L. P. Eisenhart. Pp. xii + 

 474. (London and Boston : Ginn and Co., n.d.) 

 Price 20s. 



THE well-known works of Darboux and Bianchi 

 are so excellent, each in its own way, that one 

 might be inclined to doubt whether another text-book 

 on the subject was really required — at least, for the 



