372 



NATURE 



{March i, 1877 



similar to tliat I had the pleasure to Hsten to on the occa- 

 sion of a recent visit to a highly valued friend of kindred 

 mind and pursuits. I cannot express to you how much I 

 valued the society of this amiable and distinguished man. 

 At eighty years of age he possesses the mental energies 

 of a man of forty, and retains what appears to me to 

 be the desideratum of advancing years, a mind susceptible 

 of impressions, with a power of discernment and reten- 

 tion which can only be looked for in the maturity of 

 life. Such, however, is the mind of Humboldt, perfectly 

 alive to every improvement and every development in the 

 advancement of his favourite studies." 



It is pleasant to compare this letter with one written 

 by Humboldt to Bunsen, as showing that this cordial 

 feeling was mutual between them ; in it Baron Humboldt 

 says : — 



" I cannot be grateful enough to you for having made 

 us acquainted with a man possessing so much knowledge, 

 so highly esteemed by all, so amiable, and so modest ; " 

 and he adds : " The king was enchanted by the de- 

 meanour of the great man, and Mr. Fairbairn did not like 

 less the frank and hearty demeanour of the King." 



An interesting chapter of this interesting book is that de- 

 voted to the researches for the experimental determination 

 of the influence of pressure in the process of solidification 

 as bearing upon the solution of the question of the solidity 

 or fluidity of the centre of the earth, and the thickness of 

 the earth's crust. This inquiry was instigated by the late 

 Mr. Hopkins, of Cambridge, and was carried on at Mr. 

 Fairbairn's Works at Manchester, in conjunction with Mr. 

 Joule and Prof, (now Sir William) Thomson. As the ex- 

 periments involved the submitting of various substances to 

 enormous pressures — sometimes as great as 6,000 pounds 

 upon the square inch — the mechanical fertility of Mr. Fair- 

 bairn's mind was of very great value to the investigation. 

 The results of these experiments pointed to the conclu- 

 sion that the least thickness that can be assigned to the 

 solid envelope of the earth must be considerably greater 

 than geologists have imagined it to be. This investiga- 

 tion was carried on three-and-twenty years ago, and it is 

 interesting to notice that its result corroborates in a re- 

 markable degree the conclusion which Sir William 

 Thomson enunciated at the recent meeting of the British 

 Association at Glasgow. 



As a scientific man Sir William Fairbairn held a high 

 position, he had an essentially analytical mind, seeing, by 

 an intuitive reasoning characteristic of him, into the prin- 

 ciples of things, separating essential from accidental 

 results, and thereby directing his experiments to the best 

 advantage. In 1850 he became a Fellow of the Royal 

 Society, and two years after a Corresponding Member 

 of the Institute of France. In 1861 he was the pre- 

 sident of the Manchester Literary and Philosophical 

 Society, which office he had held for five years. In i860 

 he received one of the Royal medals of the Royal Society 

 for his papers in the Philosophical T7-ansaciions, and the 

 following year he held the office of President of the British 

 Association, which met at Manchester. In considera- 

 tion of this and of his services to engineering science he 

 was ofi^ered the dignity of knighthood, which he refused. 

 Eight years after, and when in the eightieth year of his 

 age, he accepted a baronetcy which was offered him by 

 Mr. Gladstone's Government. He survived this honour 

 five years. 



A more useful and eventful life than that of Sir William 



Fairbairn rarely falls to the lot of a biographer to record- 

 The work before us shows, however, that it has fallen into 

 good hands. Dr. Pole is himself an engineer and a man 

 of science : he was associated with Sir William Fairbairn 

 in many of his works, and he possessed exceptional quali- 

 fications for teUing the story of such a life. The interest— 

 whether personal, historical, or scientific — is maintained 

 throughout the book, and as an autobiography of great 

 literary merit we would recommend it to our readers. 



C. W. c. 



GROTH'S '' CRYSTALLOGRAPHY" 

 Physikalische Krystallographie und Einleitung in die 

 krystallographische Kenntniss der wichtigeren Stib- 

 stattzen. Von P. Groth. Mit 557 Holzschnitten im 

 Text, einer Buntdruck, und 2 lithographirten Tafeln. 

 (Leipzig : Wilhelm Engelmann, 1876.) 



PROF. GROTH has written a good book on a subject 

 for which, if it attracts but few students in England, 

 German universities will supply readers. It is a good 

 book, as being written by a man whose work puts him in 

 an authoritative position for writing it, while to anyone 

 who is master of the small mathematical experience 

 needed it is eminently readable, is to the point, and not 

 too voluminous. It is moreover copiously and well illus- 

 trated. Of course, even as an Arabic chronicler of the 

 events of his time, invariably commences his history 

 with the origin of things, and the early traditions of man- 

 kind, so a German professor who writes on crystallo- 

 graphic optics, of necessity devotes a good many pages to 

 a sketch of the fundamental laws of optics and the general 

 principles of the undulatory theory. Our author, how- 

 ever, while doing so never loses sight of his purpose, 

 and a few pages so occupied are probably intended to fill 

 a void in the training of some of those for whom the book 

 is intended. 



Indeed for the student who wishes to obtain only so 

 much knowledge of the principles of physical optics as is 

 requisite for following the methods of the crystallographer, 

 it would be difficult to find a more compendious and 

 useful statement and illustration of those principles than 

 in Prof. Groth's book ; the exposition of them being so 

 completely cleared of difficult mathematical language that 

 the student might be led on to the possession of a fair 

 insight into the optical characters of a crystal without 

 any idea of the profound and splendid series of mathe- 

 matical achievements by which the theory of light has 

 been elaborated. 



Prof. Groth has dealt in a similar if less complete 

 way with the thermic properties of crystals. One might 

 perhaps have expected a fuller treatment of the subjects 

 of cohesion and cleavage, of the relations of crystals to 

 magnetism, and of the results and the best methods of 

 experimenting on pyroelectric crystals, in a treatise 

 the physical aspects of crystallography. 



What is perhaps the best part of Prof. Groth's work is • 

 the description of the instruments used by the crystallo- 

 grapher, such as the " polarisation-instrument " as he 

 calls that necessary companion which has been hitherto 

 known, under its very usual form, as a Norremberg, or as 

 a polariscope, or as a polarising microscope. This in- 

 strument has been reconstructed by our author in an 



or 



