Sei'Tk.mijkk 26, 1895] 



NA TURE 



519 



OCR HOOK SHELF. 



Die Lchre von tier Eh'ktrizitiit iind dcrcn Praktische 



Venucnditng. By Th. Scliwartze. (Leipzig : J. J. 



Weber, 1895.) 

 Thf; author in his preface says that his intention in 

 vritiny this book was to give the bearing of the latest 

 scientific results in electricity on electro-technology. He 

 goes on to say that the contents will probably appear 

 peculiar. The first of the above statements, taken in 

 conjunction with the title of the book, will probably give 

 as erroneous an idea of the contents as it is possible to 

 obtain. For if there is one thing the author does not do, 

 it is to give the bearing of the few modern discoveries, 

 or lines of thought, which he mentions on the practical 

 applications of electricity. 



For all intents and purposes the book may be divided 

 into two parts. The first of these deals with the question 

 of the fundamental principles of general 

 physics and with some mechanical problems, „ , 



such as moment of inertia, oscillations of a j 



pendulum, wave-motion, &c. The second 

 part deals more particularly with electric and 

 magnetic phenomena. 4 



Throughout the greater part of the book, 

 but particularly in the first part, the reader 

 will probably heartily endorse the authors 

 view, that the contents of the book are 

 peculiar ; for the subject of dimensions is 

 treated at great length, so that, for at any 

 rate the first three hundred pages, there is /, 



hardly a page without at least one di- ^ 



mensional equation. The appearance of 

 some of these dimensional equations, how- ^° 

 ever, are certainly peculiar, for the author 

 ■ittempts to introduce a set of dimensions 

 in terms of what he calls " Linearkraft,'' 

 " Flachcnkraft," and "\'olumenkraft." These 

 tjuantitics he indicates by the symbols L, L- 

 and L'-, regardless of the fact that in those 

 <limensional formute, in which length, mass, 

 and time are taken as the fundamental units, 

 the symbol L is used for a length. Even 

 the author himself seems to have got muddled 

 when such equations as [M-L-] = [ML'-] arc 

 allowed to appear, and the state of mind 

 of the student, whose command of dimen- 

 sions is limited, after reading the book, is 

 lamentable to think of In the chapter deal- 

 ing with the dimensions of the electrical and 

 magnetic units, no mention is made of the 

 effect of the properties of the medium, and 

 although Riicker's name is mentioned in the 

 preface in connection with the subject of 

 dimensions, no mention is made of his 

 proposal to consider the specific inductive 

 capacity and the permeability of the medium 

 as subsidiary fundamental units, and to indi- 

 cate their presence in the dimensional 

 formuke. The more purely electrical portion 

 of the book calls for little remark, and contains a some- 

 what elementary treatment of the subject of electro- 

 statics, such as the calculation of the capacity of some 

 simple forms of condensers, &c. There are also chapters 

 dealing with uni-directed currents, thermo-electricity, 

 electrolysis, electro-magnetic induction, and the dynamo. 

 Finally, about seventy pages are devoted to what is called 

 "electro-tectiniches,'' in which the commoner forms of 

 electrical measuring instruments are shortly described. 



While only a very short account is given of Hertz's 

 work, contrary to what one would e.vpect in a (German 

 work, considerable space is devoted to a description of 

 Klihu Thomson's more showy experiments with rapidly 

 alternating currents. 



NO. 1352, VOL. 52] 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither (an he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communicalions.l 



Rain in August. 



.•\rGtJST being a harvest month, and the holiday month /ar 

 excellence in this countr)', its weather is a matter of concern in 

 multitudes. I propose to show how the rainfall of .Vugust at 

 Greenwich h.is varied in the last half-century (1841-95). 



This variation appears to me rather to suggest sun-spot influ- 

 ence ; but whatever may be thought about this, it may be 

 interesting to observe how far the kind of corresponcience 

 here pointed out is maintained in the future. 



In the accompanying diagram we have (a) a dotted curve 

 showing the variatiim of .August rainfall, and the values have 



40 

 60 

 Eo 



TOO . 



cde 

 1 20 6*0 



1041 



■g '62 



71 



■7 'So 



9 92 5 



Rainfall in .August, Greenwich, a. The same, smoothed (j-.av.). b. Inverted sun-spot 

 curve. (-, ti, €. Rainfall in August at Haverfordwest, Llandudno, and Boston 

 (smoothed). 



been smoothed with averages of 5, yielding the continuous 

 curve a' . Underneath (1^) is an inverted sun-spot cur\-e. 



A considerable correspondence may here be traced, es- 

 pecially in the last three waves ; the crests or maxima of 

 ihc smoothed rainfall curve coming near the sun-spot minima, 

 and the hollows or minima of the former near the sun-spot 

 maxima. 



It seems specially noteworthy that in each year following a 

 .sun-spot maximum year we have had a ver)' dry August. Thus 

 (the August average being 2 "38) we have : 



Sun-spot max, 1S4S 



,, 1S60 



1870 



1883 



R.iinfall of .-Vugust 1S49, 0'45 in. 

 ,, ,, 1861, 0-57 ., 



l87l,o§6 ,, 

 „ „ 1SS4, 0-67 ,, 



