5io 



NATURE 



[October 19, igu 



five part in remedying this state of things, and the 

 nt volume forms the first part of a record of 

 what lie accomplished. 



The contents are arranged by the editors in sec- 

 tions, the first of which, extending to nearly 200 

 pages, is headed " Elasticity and Capillarity," and 

 contains the author's earliest published papers. The 

 two papers on capillarity, however, belong to the years 

 1906 and 1907. In the first of them, the author repro- 

 duces (he substance of a paper by Lord Rayleigh, on 

 the formation of drops, because, as he says, it had 

 been treated " etwas stiefmtitterlich " by German 

 pi riodicals, and he directs attention to the value of the 

 "method of dimensions" used by Lord Rayleigh. 



The second section, nearly 100 pages, relating to 

 " Heat, Thermoelectricity, and Gaseous Mechanics," 

 contains almost the only exclusively theoretical paper 

 in the volume. In this paper, Kohlrausch starts from 

 the fact that differences of temperature between 

 neighbouring parts of continuous pieces of metal are 

 an essential condition of the action of a thermo- 

 electric couple. He points out that a thermoelectric 

 current is therefore necessarily accompanied by a 

 current of heat, and, assuming a mutual convective 

 action between these two currents — that an electric 

 current conveys heat and that a current of heat con- 

 veys electricity — and assuming further that the quan- 

 tity of electricity conveyed by a given How of heat 

 depends on the temperature of the conductor, he 

 arrives at the ordinary formula, which represents the 

 electromotive force of a thermoelectric couple as being 

 proportional to the difference of temperature of the 

 junctions multiplied by the difference between their 

 mean temperature and a fixed temperature depending 

 on the nature of the couple. 



The third section, fifty pages, devoted to "Optics," 

 deals chiefly with a method of measuring indices of 

 refraction founded on the phenomenon of total reflec- 

 tion. 



The fourth section, more than 650 pages, "Elec- 

 trical and Magnetic (absolute) Measurements and 

 Methods of Measurement," is the most important in 

 the book. We may mention specially a paper on the 

 "Absolute Value of Siemens's Unit of Resistance," 

 which contains an acute and interesting criticism of 

 the experiments of the British Association Committee. 

 Unfortunately, in his own experiments, Kohlrausch 

 adopted, without personally verifying them, the 

 dimensions of a coil that had been wound bv Weber, 

 although he carefully determined every other quantity 

 involved, with the consequence that he obtained an 

 erroneous result. A later determination of the "Abso- 

 lute Resistance of Mercury " led almost exactly to 

 the value now adopted as the most accurate. The 

 same may be said of a determination of the " Electro- 

 chemical Equivalent ol Silver," which he carried out 

 in conjunction with his brother YVilhelm. These two 

 investigations seem to have been conducted with the 

 ill most care, and they afford striking examples of the 

 multitude of minute precautions that must be observed 

 n great accuracy is aimed at in the determination 

 of a physical constant. These two papers are the 

 most elaborate in the volume, but all go to show the 

 author's love ol exact measurement and furnish 

 NO. 2190, VOL. 87] 



evidence that he was pre-eminently in his right place 

 when he was appointed president of the Reichsanstalt. 



A final section, 100 pages, is headed " Miscellnm »i. 

 and Books." It contains some interesting addresses 

 and reports and biographical notices, and the preface 

 to the last (eleventh) edition of the author's " Lehr- 

 buch der praktischen Physik," first published in 1870, 

 under the title " Leitfaden der praktischen Physik." 



It only remains to add that the volume is excel. 

 lentlv printed and very carefullv edited. 



G. C. F. 



A MODERN HISTORY OF CHEMISTRY. 

 A Concise History of Chemistry. By T. P. Hilditch. 

 Pp. ix + 263. (London : Mcthuen and Co., Ltd., n.d.) 

 Price 2s. 6d. 



IN this book an attempt is made to trace the 

 development of chemistry from the point of view 

 of its present-day position — that is, from the point of 

 view, say, of a traveller who, having reached his goal, 

 seeks to retrace his route, and to survey, as if from 

 an eminence, the devious and dimly indicated wander- 

 ings by which he has attained the coign of vantage he 

 has gained. There are, of course, two ways of 

 writing history. The first, which is by far the more 

 difficult, inasmuch as it presupposes profound know- 

 ledge and extensive research, combined with imagina- 

 tion and the faculty of detachment, is for the historian 

 to seek to project himself, as it were, into the parti- 

 cular period with which he is dealing at the moment, 

 and to attempt to elucidate it from the contemporary 

 point of view. In this way he becomes a faithful 

 chronicler of the epoch, reflecting its spirit, correcting 

 its errors, supplementing its truths, and making mani- 

 fest the gradual evolution and enlargement of the 

 special phase of intellectual, moral, social, or political 

 development with which he may be concerned. Or he 

 may, as in the present case, view the whole course 

 retrospectively. This, no doubt, has certain advan- 

 tages. But when applied to chemistry it is apt to do 

 an injustice to one's predecessors by belittling their 

 successive contributions to the general knowledge : 

 there is apparently so much chaff to be winnowed, and 

 the kernels of good grain would seem to be so few 

 and so small in comparison with the harvest of to-day. 

 It is apt, too, to give false impressions of the course 

 of reasoning — the movement of the time — by which 

 the early speculators were led to formulate their 

 attempts at a chemical system. It is impossible to do 

 full justice to their efforts unless the historian has 

 that complete sympathy with them which comes from 

 trying to put himself in their place, and so appreciat- 

 ing the motives by which they were guided or 

 impelled. 



In a volume of some 250 small octavo pages, which 

 seeks to trace, in the broadest possible outline, the 

 growth of chemistry from the earliest times to the 

 present epoch, there is not much room for dwelling 

 on the philosophy of its history. Mr. Hilditch is 

 chiefly concerned more with results than with motives 

 - with the ordering in historical sequence — of the 

 significant facts of the science, and it is quite remark- 

 able what a number of such facts he has contrived to 



