H4 



NATURE 



\yune 24, 1875 



molecule must melt at the same instant, and so on to the 

 other end of the glacier, which is absurd ; and besides, 

 what is there in this theory to distinguish a glacier from a 

 common piece of ice ? which on this principle ought to 

 flatten out and not retain its shape as it does. Why also 

 are we to suppose the molecule alternately to melt and 

 crystallise when the heat is continuous ? The mistake 

 on which this explanation is founded seems to be the 

 confounding of radiation with conduction. It is radiant 

 heat that passes through ice, which is a very bad con- 

 ductor. Ice at 32° F., heated by conduction, would cer- 

 tainly melt on the outside ; the interior can only melt by 

 the absorptiofi of radiant heat. We cannot either under- 

 stand the statement "that ice at 32° cannot take on 

 energy from a heated body without melting," unless it is 

 the exact equivalent of what we have just said ; but then 

 no heat could be transmitted, as it would be consumed in 

 melting the ice, and if it were otherwise, still any amount 

 of heat short of the latent heat of water might be " taken 

 on " by a molecule without melting it. 



We fear, then, that the complete account of the descent 

 of a glacier is still a desideratum. The various theories 

 may contain elements of truth, but none are entirely satis- 

 factory. 



As far as definite results are concerned, it will appear 

 that Mr. CroU's book does not do all he hopes it may, yet 

 we welcome heartily his attempts at reducing complex quer. 

 tions to arithmetical issues, for we thereby gain clearer 

 ideas as to whereabouts the truth may lie, and certainly 

 have the questions put before us in a more definite form. 

 The vast problems with which he deals, and for the 

 suggestion and discussion of which science is so largely 

 indebted to him, are waiting for solution, and every 

 attempt is valuable, both as showing us where to look 

 and where not to look for help. 



J. F. B. 



SPR AGUES ELECTRICITY 

 Electricity J its Theory, Sources, and A'bplications. By 

 John T. Sprague. (London : E. and F. N. Spon, 

 1875.) 



THE author tells us in his preface that this book is 

 "written chiefly for that large and increasing class 

 of thinking people who find pleasure in the study of 

 science, and seek to obtain a full and accurate scientific 

 knowledge for its own sake, or as part of the necessary 

 mental preparation for many of the departments of modern 

 life." Our examination of the book itself would lead us 

 to an opposite conclusion. We very much question 

 whether any one of the class to whom the author refers 

 will ever have the patience to read through this volume. 

 Certainly they will have but sorry pleasure and any- 

 thing but full and accurate information. The book 

 abounds in foolish conceits advanced with a show of 

 knowledge that cannot but repel every intelligent reader. 

 That we are justified in these strictures will be seen 

 from one or two quotations. Here, for example, are some 

 statements taken from chapter ii. in this book. At the 

 outset the author asserts that the fundamental facts 

 relating to frictional electricity given in " one of our 

 standard electrical works (and it is just what all say) . . . 

 are received as absolute truth by electricians . . . and 



yet there is scarcely a truth in them which is not over- 

 weighted by an error, and the simplest facts even are 

 erroneously stated " (p. 17). Mr. Sprague, so far as we 

 are aware, has never done anything to prove that he is 

 able to sit in judgment on the intellectual giants among 

 modern men of science. Mere off-hand condemnation 

 of the laborious work of men like Sir W. Thomson and 

 Prof. Clerk-Maxwell cannot for one moment be tolerated. 

 Mr. Sprague seems to us to be like a child trying 

 to turn one of the pryamids of Egypt upside down 

 because he imagines it has been built the wrong way 

 up. The best teaching is to let him try. This is 

 how the author proceeds in his bold attempt. It is not 

 true, he states, that bodies similarly electrified repel 

 each other ; " the repulsion is only apparent ; the real 

 cause of the motion is to be found in the attraction 

 exerted by surrounding bodies." (p. 19). And with regard 

 to the electrophorus, " that the dish forms the conductor 

 from the dielectric to the earth, as all electrical books tell 

 us, is an error which will come up for examination by 

 and by" (p. 15). 



According to Mr. Sprague the common explanation of 

 induction is all wrong ; " the real explanation is " given by 

 him (p. 49). The rubber of an electric machine " is seldom 

 made upon true principles " (p. 33) ; and as for the earth- 

 connection to an electric machine, we are assured that it 

 is merely imaginary ; what we must do is to lead a chain 

 to the floor or gas-pipe, and " hence the idea that we 

 make a connection with the mass or surface of the earth " 

 (p. 29). And further on (p. 40) we read— still concerning 

 the machine — that " because both the poles are insulated 

 and the circuits limited, we are freed from the ignis 

 fatmis of the earth-connection." We presume the 

 author does not mean the earth-connection is an ignis 

 fatuus, but that the usual explanation is such ; it is 

 evidently so to him, for it has landed Mr. Sprague in a 

 quagmire of crudities where we will not attempt to follow 

 him. In these early chapters everything is attributed to 

 " polarisation," a word which has for the author a con- 

 soling sound like that " blessed word Mesopotamia." We 

 are told that it is for a similar cabalistic reason elec- 

 tricians employ the term " potential." Not understanding 

 the term, and yet finding it necessary to say something 

 about it, this is how the author discusses the subject : 

 " The word [potential] is always used in place of tension 

 or electro-motive force, because there is something full 

 and smooth sounding about it ; but the idea which really 

 does belong to it is a pure mathematical abstraction 

 which only highly trained minds can apprehend" (p. 154). 



In another part of this book we meet with dark hints 

 upon " Sprague's patent universal galvanometer," an in- 

 strument that is to " do for many purposes, without other 

 instruments and without calculations, the work which at 

 present requires the Wheatstone's bridge and expensive 

 resistance coils, as well as many calculations." But, be- 

 yond exciting our curiosity, the author declines to go 

 further, and so we cannot give our readers the benefit of 

 this wonderful galvanometer, which combines " Pyscho " 

 and " George Bidder " in one. 



Notwithstanding the grave defects that quite spoil the 

 early chapters in this book, it is only just to the author to 

 point out that the latter part of the volume has conside- 

 rable merit. Much useful practical information is to be 



