'52 



NA TURE 



[August 5, igog 



loudlv for revision. This is tlie ahva}* recurrent 

 objection to the encyclopaedia, which applies with 

 special force to an encyclopaedia of so progressive an 

 industry as the electrical. If any real attempt is to 

 be made to maintain such a publication in the front 

 rank, it can only be done by very frequent and 

 thorough revision. We have certainly no ground for 

 complaint in the present instance on the score of 

 frequency of revision — a new edition within four 

 years of the original issue is as much or even more 

 than could be expected^but some of the contributors 

 do not appear to have taken the dut)' of revision 

 with sufificient seriousness, and thus, whereas some 

 of the articles have been entirely rewritten, others in 

 which progress has certainly been no less marked 

 appear to have been scarcely altered. 



We need make no apology in this connection for 

 referring to the articles on electric lamps. Probably 

 in no other branch of the electrical industry has there 

 been more startling progress duiing the past three or 

 four years. Often though the expression is abused, 

 it is true in this instance to say that both arc lighting 

 and incandescent lighting are being revolutionispd. 

 The article on incandescent lamps has been brought 

 well up to date, and the information given on metallic 

 filament lamps, if not so full as some could hope, is 

 as full as could be expected in relation to an industry 

 slill carried on with more or less secrecv ; but the 

 article on arc lamps appears to be untouched. We 

 have the gravest suspicion that the author does not 

 realise what the flame arc really is ; if he does, he 

 signally fails to convey a correct impression to his 

 readers, and, at the best, his treatment of the flame 

 lamp is grossly inadequate. 



In reviewing one of the volumes on its first appear- 

 ance we ventured to suggest that, in view of the 

 generally inferior standard of the letterpress as com- 

 pared with the illustrations, the latter should be pub- 

 lished without the former. The publishers appear to 

 have adopted this suggestion to the extent of attaching 

 to the inside of the back covers of some of the volumes 

 ingenious little folding paper models of electrical ap- 

 paratus to which we have been unable to trace any 

 reference in the text. Many a pleasant half-hour mav 

 be spent by the student of electrical engineering, 

 unable to obtai.i access to real electrical apparatus, in 

 unfolding these models and trying to fold them up 

 again in the correct order. 



We are at a loss what to say in conclusion ; we 

 suppose that, so long as there is a large number of 

 engineers anxious to write, and several willing to 

 read, there will be an output of treatises, good, bad, 

 and indifferent; but, personally, we have a strong 

 disposition against buying in bulk, taking the good 

 with the bad, "as they come," in the phrase of the 

 market. 



The beneficent uncle anxious to make a suitable 

 gift to a budding electrical ergineer may find in these 

 volumes a useful outlet for surplus wealth, but the 

 discriminating student will be well advised to make 

 other investments. We can well imagine that there 

 will be many, when confronted with so imposing an 

 array of information in so handsome a guise, who will 

 NO. 2075, \OL. 81J 



be unable to believe that the matter can be less good 

 than the manner; but we are loth to think that it is a 

 co;nprehensive treatise such as this which really re- 

 presents what the electrician wants. 



M.M'RICE SOLO.MO. 



THE IHERMODYSAMICS OF THE EARTH. 



Radio-activity ami Geology. By Prof. J. Joly, F.R.S. 

 Pp. xi + 287. (London : A. Constable and Co., Ltd., 

 1909.) Price 7.s~. 6d. net. 



THO.SE who are acquainted with Prof. Joly's presi- 

 dential address to Section C at Dublin last year 

 will not be surprised at the appearance of this volume 

 from his pen. One of the most remarkable chapters 

 the scientific historian has yet to write is the story of 

 the rapid progress of research into the phenomena of 

 atomic instability. In the spontaneous disruption of 

 atoms, showing itself in the phenomena of radio- 

 activity, we have learned of a store of energy of im- 

 mense magnitude hitherto undreamt of. The fact 

 alone that atoms are unstable systems has enlarged 

 immeasurablv the scope of our speculations regarding 

 all inorganic evolution, while the knowledge of the 

 forces locked up in them has still more directly alTected 

 almost every department of science. It is impossible 

 that the geologist should long remain indifferent to 

 this new phase of scientific inquiry, and it is Prof. 

 Jolv's endeavour to show him that already he must give 

 heed to its teachings, and to point out where atten- 

 tion must be given. As being himself an active in- 

 vestigator, able both as physicist and geologist, no one 

 better qualified for the task could be found, and his 

 work must be carefully considered by every thoughtful 

 geologist, however much an}' of his conclusions may 

 be controverted. 



The volume is wisely opened with a couple of 

 chapters in which the fundamental principles and 

 methods of radio-active inquiry are simply but ac- 

 curately explained. These we wc uld especially commend 

 to the reader who may be inclined to a not unnatural 

 scepticism as to the trustworthiness of conclusions 

 based on the investigations of quantities of material 

 habitually measured in billionths of a gram. It is of 

 the utmost importance, too, for the geologist to realise 

 to what degree the intra-atomic changes are indepen- 

 dent of physical conditions, and that such changes do 

 not affect the atoms of radium alone, but in varying 

 degiees those of many substances. 



In the chapter on radium in the earth's surface 

 materials we are supplied with fairly ample data on 

 which to judge of the general distribution of this 

 element and its associates in the rocks. It is a sig- 

 nificant fact that the rarer an element the more uni- 

 formly it appears to be distributed in nature. In spite 

 of the natural variation of the quantities in different 

 rock-specimens, and of considerable divergence among 

 the averages of different investigators, we are still 

 left with the conviction that the almost uniform 

 presence of radium in fairly well ascertained quantity 

 throughout the earth's crust is assured, and may be 

 safely assumed as a basis of speculation. The 



