August 2, 1877I 



NA TURE 



263 



not read the book with admiration. Like all Mr. Lewes' 

 works, it is a repertory of suggestive fact and of equally 

 valuable and suggestive thought ; and if any reader 

 derive from its perusal a tithe of the intellectual stimula- 

 tion it has afiforded me, he may regard his time as well 

 spent. Reflective minds are diligently working towards 

 clearer conceptions in a region that has hitherto been all 

 obscurity. There is reason to believe that ere long philo- 

 sophic thinkers of the highest rank will for the first time 

 agree as to one or two fundamental conceptions. Few 

 living men have done as much as Mr. Lewes to usher in 

 this new era. Knowing my criticisms to be inspired 

 solely by the same impersonal motives by which he has 

 himself been sustained throughout his extensive labours, 

 I am sure Mr. Lewes would be the last person to suggest 

 that I could have made better use of the space at my 

 ci>posal. Others, better qualified than myself, will draw 

 attention to the importance of those parts of the work that 

 I have not mentioned, as, for instance, the splendid essay 

 on the Nervous Mechanism. 



Douglas A. Spalding 



GORE'S "ELECTRO-METALLURGY" 



The Art of Ekctro-Mctallurgy j [iiuiuding all known 

 Processes of Electro-deposition. By G. Gore, LL.D.^ 

 F.R.S. Text-books of Science Series. (London : 

 Longmans, Green, and Co., 1877.) 



DR. GORE has evidently spared no pains to make 

 this text-book a complete manual of the art of 

 electro-metallurgy. Beginning with the history of the 

 subject, he gives an interesting account of the rise and 

 development of the art, full of names and dates and 

 references, and makes the early inventors tell, as far as 

 may be, their own story by quoting freely from their 

 published papers. Then comes a " theoretical division," 

 about which we have something to say presently, and 

 this is followed by what forms the greater part of the 

 work — a detailed account of practical methods of deposit- 

 ing the various metals. This portion of the book, at once 

 thoroughly circumstantial and comprehensive, cannot fail 

 to prove most usefuljto the practical electroplater as well 

 as to the scientific student. The metals most commonly 

 employed in the arts receive, of course, most attention ; 

 but almost none, even of the rarest metals, pass without 

 notice, and the experiments are described with the pre- 

 cision that comes only of experience. An admirable 

 feature of Dr. Gore's book is the habit he has of giving 

 specific references to the authorities he makes use of, so 

 that any one with a library at his command may, if he 

 choose, turn up the passages cited. The remainder of 

 the book is filled by a "special technical section" con- 

 taining various practical directions and details, and, in 

 conclusion, we have a list of the books previously published 

 on the subject and of the English patents referring to 

 electro-metallurgy. The author is to be congratulated on 

 the accumulation and systematic arrangement of an im- 

 mense mass of information of a kind that will be welcomed 

 alike in the workshop and]in the laboratory. 



If Dr. Gore had given us only the practical parts of his 

 book we should have had little to say beyond praise and 

 thanks. Unluckily, however, for himself as well as for 



his readers, he has" introduced a chapter on the theoretical 

 principles which underlie the art of electro-deposition. 

 Such theoretical rechauffes are often to be found in prac- 

 tical text-books, but their existence is surely a thing to be 

 protested against even when they are tolerably well writ- 

 ten. No one can hope to give a satisfactory account of 

 chemical and electrical theory in fifty pages, and when 

 his work is to form one of a series in which chemistry 

 and electricity have already been treated of in separate 

 books, the attempt is not only useless but unnecessary. 

 These short abstracts are certainly not to be recom- 

 mended to the novice ; and to the student who has already 

 studied the subjects at greater length they are little short 

 of an impertinence. In a book which stands by itself 

 they might be tolerated if they were at once concise and 

 accurate, giving what is needed and no more. In the 

 case before us these extenuating circumstances are all 

 absent. That Dr. Gore's "theoretical division" is not 

 concise the following quotation will suffice to show : — 



" The strength of the current is equal to the electro- 

 motive force divided by the resistance ; this is known as 

 Ohm's law ; it is directly proportional to the electro- 

 motive force, and inversely proportional to the resistance ; 

 if the resistance remains the same, and the electromotive 

 force varies, the strength is directly proportional to the 

 electromotive force ; and if the electromotive force 

 remains the same, and the resistance varies, it is inversely 

 proportional to the whole of the resistance in the circuit " 

 (p. 71)- 



As an instance of matter which might very well have 

 been left out, take the following. After giving a table of 

 conductivities. Dr. Gore proceeds : — 



" If the conduction-resistance of distilled water is so 

 great in relation to that of copper, we can easily un- 

 understand, by referring to the previous table, that the 

 resistance of gases must be enormous. The electric 

 conduction-resistance of air heated 'to redness {sic) is 

 30,000 greater than that of water, containing a 20,000th 

 part of its weight of sulphate of copper m solution " 

 (P- 31). 



Why this long-buried result of E. Becquerel's (here, by 

 the way, the authority is not cited) should be unearthed 

 for^the benefit of students of electro-metallurgy is almost 

 as puzzling as is the strange piece of d. priori reasoning 

 in the first sentence, which, it is distressing to find, we 

 are expected to understand easily. 



The ivagueness'and inaccuracy of some parts beggar 

 criticism, and leave the reviewer but one weapon — a 

 severe one indeed, but he has no other — he can only 

 quote. Here are a few specimens chosen almost at 

 random. 



" The fundamental act or principle 01 magneto-electric 



action is, wherever there is varyins; niagnetistn, there is 

 an electric current induced in an adjacent closed circuit at 

 right angles to it" (p. 57) ; the italics are the author's. 



''The electromotive force, or strength of the current to 

 overcome resistance, depends upon the degree of differ- 

 ence of strength of chemical affinity of the two metals for 

 the electro-negative constituents of the liquid" (p. 70). 



"The electromotive force (commonly called 'the 

 intensity ') of the[;current ..." (p. 337). 



" As tlie electromotive force is diminished by resistance, 

 a diminution of resistance in any part of the circuit will 

 increase it" (p. 337) ; this extract we have ventured to 

 Italicise. 



" Motion of the articles is very advantageous ... it 



