NATURE 



509 



THURSDAY, OCTOBER 19, 191 1. 



,1 VOLUME OF KOHLRAUSCH'S COLLECTED 



PAPERS. 

 Gesammelte Abhandlungen von Friedrich Kohlrausch. 



Erster Band, Elastizitat, Warme, Optik, absolute 



elektrische Messungen und Verschiedenes. Pp. 



xxxv+1108. (Leipzig: J. A. Barth, 1910.) Price 



25 marks. 



THE first paper contained in this collection is dated 

 1863, the last is dated 1909, less than six months 

 before the author's death. Together they fill more than 

 one thousand pages, and each of them has its own 

 value and interest. When it is considered that the 

 present volume contains none of the work on the 

 conductivity of electrolytes and mobility of ions, in 

 connection with which it is probable that the author's 

 name is best known (the papers on these subjects 

 being reserved for a second volume), it must be 

 admitted that here is remarkable evidence of sustained 

 and well-directed labour. 



The half-century that was nearly covered by Kohl- 

 rausch 's scientific activity was, in relation especially 

 to magnetism and electricity, the subjects at which 

 he chiefly worked, a period of systematising and set- 

 ting in order, rather than, until near the end, of the 

 discovery of new phenomena leading to essentially 

 new conceptions. Even the reconstruction of elec- 

 trical theory bv Maxwell was based, not on new dis- 

 coveries, but on a revised interpretation of well-known 

 facts. To those whose personal memory of such 

 things goes back to Kohlrausch's student days, the 

 greatest and most far-reaching of the changes they 

 have lived through must seem to be the universal 

 recognition of the principle of the conservation of 

 energy, and, as essential for the definite statement 

 of this principle, the introduction of the conception 

 of "absolute" units of measurement. 



At the time of which we speak, these ideas had 

 been formulated, but they were far from familiar, and 

 the instrumental appliances needed for their practical 

 application scarcely existed. Gauss's method of 

 measuring the absolute intensity of the earth's mag- 

 netic field was beginning to find a place in German 

 text-books, but it might be sought in vain in Eng- 

 lish or French books. A tangent-galvanometer of 

 accurately known dimensions was a rarity. " Resist- 

 ance-boxes " did not exist. Kirchhoff had, as long 

 ago as 1849, published the experiments that are com- 

 monly cited as constituting the earliest actual 

 measurement of a resistance in absolute measure, but 

 no concrete embodiment of his results existed. 

 Wilhelm Weber had distributed a certain number of 

 coils of which he had measured the resistance, but 

 very few physicists possessed a coil, or wire of any 

 kind, of which they knew the resistance, otherwise 

 than by comparison with some accidental arbitrary 

 standard. Though the fundamental principles of 

 absolute measurement are due undoubtedly to Gauss 

 and Wilhelm Weber, the general spread of the con- 

 ception and the introduction of practical methods 

 founded thereon was, in a great degree, promoted by 

 NO. 2190, VOL. 87] 



the Committee on Standards of Electrical Resistance 

 first appointed by the British Association in 1861. 

 The committee's first experimental determination of 



the " B.A. unit," io r - — , , was published in 1S63. 

 second J 



At the same time, Maxwell and Jenkin's memorable 

 paper "On the Elementary Relations between Elec- 

 trical Measurements " appeared. As the first con- 

 nected and comprehensive statement of the matter, 

 this paper contributed greatly to promote a more 

 general understanding of absolute measurements. 



It is significant of the condition of the current 

 teaching of theoretical physics at this time that, when 

 Tyndall published his " Heat as a Mode of Motion " 

 in 1S63, he introduced it as an attempt "to bring 

 the rudiments of a new philosophy within the reach 

 of a person of ordinary intelligence and culture," 

 but he and other popular writers so completely 

 neglected to deal with one-half of the new philosophy 

 that Macquorn Rankine felt called upon, in 1867, to 

 publish a paper, " De la necessity de vulgariser la 

 seconde loi de la thermodynamique." There was no 

 such thing in those days as a physical laboratory in 

 the modern sense of the word. As Kohlrausch says, 

 conditions were "pinched and patriarchal," and it 

 was quite appropriately that the whole instrumental 

 outfit of a university was called the "physical 

 cabinet." 



The state of electrical knowledge at the outset of 

 Kohlrausch's career is well brought out by him in 

 speaking of the conditions under which Gustav 

 Wiedemann wrote his magnificent " Lehre vom Gal- 

 vanismus und Elektromagnetismus," first published 

 from 1861 to 1863 : — 



"It is onlv right that we should call to mind some 

 of the inherent difficulties which beset the production 

 of this classical work, difficulties which increased the 

 labour of the exposition to an extent that we can 

 understand only by a distinct effort of the imagina- 

 tion. 



"The thermodynamic basis for the connecting links 

 which now bind all together to a coherent whole was 

 then in course of development, and had not by any 

 means become common property; and in the case of 

 electricity especially a consistent system of measure- 

 ment was still wanting in a practically accessible 

 shape. It is true that Ohm and Kirchhoff had laid 

 down the laws of the strength of currents, and the 

 foundations of a system of measurement for current, 

 tension, and resistance had been settled by Gauss and 

 Weber, but hitherto very few measurements in 

 definite units had been actually carried out. It is 

 hardlv too much to say that the subject of absolute 

 electrical measurement was as yet familiar to but few 

 physicists. The Daniell's cell was almost the only 

 standard of measurement that was commonly access- 

 ible. Measuring instruments that gave the strength 

 of a current in" intelligible units were not introduced 

 till much later. The measurements of resistance then 

 in use were .inconvenient and untrustworthy. I re- 

 member my own not very successful struggles with 

 file and plane to construct a rheostat. The statements 

 given in published papers in reference to the units of 

 resistance employed were often uncertain to the 

 extent of 50 per cent, or more." 



As was befitting in a son of Rudolf Kohlrausch and 

 a pupil of Wilhelm Weber, our author took an effec- 



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