September 2, 1915] 



NATURE 



so as to give a complete analysis of the losses in 

 about half an hour after getting the machines 

 into a steady condition. 



We are flattered by the graceful acknowledg- 

 ment that our mode of numbering the illustrations 

 has been adopted, but we would have greatly 

 preferred that in a much more important direction 

 the author had followed the methods we advocate, 

 but cannot claim to have originated. We refer 

 to the practice of making the algebraic symbols 

 stand for things and not merely for numbers, so 

 that the formulas will apply irrespective of units. 

 Mr. Maccall seems unable to discuss principles 

 apart from some particular units, with the result 

 that his mathematics is horribly complicated by 

 numbers which have nothing to do with the facts, 

 but arise from the unfortunate, although perhaps 

 customary, choice of units. In some cases we 

 are treated to separate deductions of formulas for 

 inch and metric measure, instead of one formula 

 with two sets of constants. As we said on a 

 former occasion, the laws of nature were exactly 

 the same ages before man ever discovered any- 

 thing about them, much less invented units in 

 which to express his measurements concerning 

 them. Make the symbols stand for things and 

 the units will look after themselves. Formulas 

 will then represent facts, and not merely parti- 

 cular numerical relations. 



W^e like the author's special symbol for 

 "number of turns," but we object to making his 

 other new symbol do double duty by using it 

 both for "current X turns " and for the name of 

 the unit "ampere-turn." 



For the new edition, which we confidently 

 expect, we hope that the publishers will adopt a 

 paper suitable for reproducing the half-tone 

 blocks. Fortunately, these form only a small pro- 

 portion of the illustrations, but where they do 

 occur they entirely spoil the appearance of the 

 book, while at the same time they are seldom 

 sufficiently distinct to be of any real use. 



(2) "Single-phase Electric Railways" gives an 

 outline description, with leading data, of all the 

 important lines of this type which have so far 

 been constructed. Although most of the matter 

 has already been published in the columns of the 

 Engineer, it is convenient to have it all collected 

 together for ready reference. For that reason, 

 it is unfortunate that the author has decided not 

 to deal fully with the motor itself, and also that 

 he has not included a great deal more data re- 

 i^'^arding the operating costs, of which much has 

 been made public during the past few years. 



The book is abundantly and well illustrated by 

 drawings and photographs; indeed, the latter take 

 such a very prominent place as to almost form 

 NO. 2392, VOL. 96] 



the raison d'itre of the book. The overhead con- 

 struction is taken in fairly full detail, but the 

 particulars of the motors and controlling gear *are 

 somewhat meagre. Diagrams of connections are 

 certainly there, but the written description is 

 generally too slight, except for the expert. 



The first chapter of three pages is mainly his- 

 torical, but just touches on the thorny battle ot 

 the systems. More eloquent than all the opinions 

 of the author and the experts is the fact, brought 

 out in a recent number of the General Electric 

 Review, that since the advent of the high-voltage 

 continuous-current system, the mileage of single- 

 phase railways has been practically stationary, 

 while that of the continuous-current system has 

 gone up by leaps and bounds, and now far sur- 

 passes its rival. It would have been far better 

 if this chapter had given an account of the general 

 principles underlying single-phase railway work- 

 ing, and a closely reasoned account of the difficul- 

 ties arising from it, the way in which these have 

 been overcome, and the relative advantages and 

 disadvantages of the system. A comparison of 

 the solutions found for these difficulties in the 

 various lines described further on would have 

 served to weld the book into a homogeneous 

 whole, instead of leaving it in twenty-three water- 

 tight compartments (one for each line described), 

 with no connection between them but the common 

 title to the whole book. 



We may conclude by saying that to the expert 

 and to the student of railway engineering, the 

 book will be of especial value as a work of refer- 

 ence, diminished although that is by the lack of 

 references to other publications. Others may find 

 it interesting, for the style is good and the matter 

 is made as readable as a catalogue (for such it 

 really is) well can be. David Robertson. 



THE LIMITATIONS OF SCIENCE. 

 (i) The Limitations of Science. By Prof. L. T. 



More. Pp. vii + 268. (New York: H. Holt 



and Co., 1915.) Price $1.50 net. 

 (2) The Magic of Experience. A Contribution to 



the Theory of Knowledge. By H. Stanley 



Redgrove. Pp. xv+iii. (London: J. M. 



Dent and Sons, Ltd., 1915.) Price 2s. 6d. net. 

 (i) r)ROF. MORE has written a study from a 

 Ji conservative point of view of the limita- 

 tions of science as shown in modern physical 

 views. "Will the results of experiment made 

 objectively which must, however, be interpreted 

 subjectively, fail in their turn as criteria of 

 truth?" (p. 2). "Science, . . . like philosophy, 

 has no ontological value. Should not the men of 

 science clearly recognise this fact, and confine 



