NATURE 



60 1 



THURSDAY, APRIL 27, 1899. 



A HISTORY OF PHYSICS. 

 A History of Physics. By Prof. Florian Cajori. 

 Pp. viii + 322. (London : Macmillan and Co., Ltd., 

 1899.) 



IT is a formidable undertaking to write a book on 

 the history of physics beginning with the dawn of 

 science and including helium and Rontgen rays, and the 

 task does not become easier when the whole has to be 

 condensed into the narrow limits of 300 pages. We 

 possess a number of more extensive histories, such as 

 Heller and Rosenberger, and a few most valuable 

 biographies of eminent men. These are boiled down 

 into the present volume, which is readable and generally 

 accurate, but is too slight and superficial to serve any 

 useful purpose. The study of the history of science is 

 of the greatest importance to the scientific man, and in 

 addition, it is, when properly treated, a most fascinating 

 study ; but when we come to estimate the value of any 

 particular treatise, we must ask ourselves what it is pre- 

 cisely in the historical treatment that interests us. For 

 when we wish to boil down our information we must 

 know what has to be retained and what may be rejected, 

 or else w-e should commit the error of imitating the 

 manufacturer of meat extracts, who retains only the 

 gelatine and water. That is, in my opinion, what Mr. 

 Cajori has done. It may be his misfortune rather than 

 his fault that the editor of N.ature has entrusted this 

 review to me ; but having always taken a considerable 

 interest in historical questions, I must acknowledge the 

 authors reading and learning while I question his 

 judgment. That, of course, may be a matter of opinion. 

 The value of historical studies seems to me to lie in two 

 directions. It is of high interest to follow out the 

 evolution of thought, the gradual development of ideas, 

 from the first suspicion of a new truth to its final ex- 

 perimental proof or mathematical demonstration. The 

 way especially in which the same idea constantly origin- 

 ates simultaneously in different minds, and the question 

 how far the different view often adopted by different 

 nations is purely a matter of education, or has some 

 deeper cause, has never yet been fully developed. 



But, quite apart from this, every reader of original 

 papers knows how many points are always missed by 

 subsequent writers, and how clear ideas are only obtained 

 by a study of original sources. If, for instance, we only 

 know Faraday, or Maxwell, or Hertz through modern 

 text-books, however good these may be, we shall miss a 

 large number of important suggestions. Led by these 

 considerations, Prof. Ostwald has originated the re- 

 printing of important treatises under the name of 

 " Klassiker der exacten Wissenschaften," and in the 

 announcement of this publication has regretted the 

 neglect of historical studies. 



Curiously enough, Prof Cajori quotes this regret of 

 Ostwald's, and expresses the hope " that the survey of the 

 progress of physics here presented, may assist in remedy- 

 ing this defect so clearly pointed out by Prof. Ostwald.'' 

 As a matter of fact, Ostwald's remedy for what he terms 

 the "absence of the historical sense," lies in the reading 

 NO. 1539, VOL. 59] 



of original memoirs, while Prof Cajori's cure lies in the 

 prescription of small homoeopathic globules intended to 

 contain the concentrated concoction of all that is 

 essential ; but whether this intention can be realised or 

 not is exactly what is open to doubt. I must justify the 

 opinion I have expressed by a few e.xamples of Prof. 

 Cajori's style and manner of treatment. I take in the 

 first instance the reference to the second law of thermo- 

 dynamics. 



"In February 1850, Rudolph Clausius ('1822-1888) 

 communicated to the Berlin Academy a paper on the 

 same subject, which contains the Protean second law of 

 thermodynamics : 'Heat cannot of itself pass from a colder 

 to a hotter body.' ... In March 1851, there appeared 

 a paper by \Vm. Thomson, which contained a perfectly 

 rigorous proof of the second law. He obtained it before 

 he had seen the researches of Clausius. The statement 

 of this law, as given by Clausius, has been much criticised, 

 particularly by Rankme, Theodor Wand, P. G. Tait and 

 Tolver Preston. Repeated efforts to deduce it from 

 general mechanical principles have remained fruitless. 

 The science of thermodynamics was developed with great 

 success by Thomson, Clausius, and Rankine. As early 

 as 1852, Thomson discovered the law of dissipation of 

 energy, discovered at a later period also by Clausius. " 



Apart from the fact that Clausius' paper of 1850 does 

 not either contain the words quoted, nor any reference to 

 a second law at all fthough the substance of it is given 

 in the paper), one would like to know to whom the in- 

 formation given in the passage can be of any use. If a 

 student possesses no knowledge of thermodynamics, he 

 will not be any the wiser by it ; and if he does, he must 

 have read books, such as Maxwell's "Theory of Heat," 

 or Baynes' " Thermodynamics," and in any of these he will 

 find much more ample and accurate historical references 

 than those given by Mr. Cajori. In the same way 

 throughout the book, the author generally does not go 

 beyond what ought to be, and often is given in the 

 ordinary text-books. As an example how short state- 

 ments, though correct, often convey incorrect ideas, I 

 give the account of the historical evolution of the ohm : 



"In 1861 the British Association and Royal Society of 

 London appointed a committee, with Lord Kelvin at its 

 head, to recommend a unit ( ' B.A.' unit ). Weber's 

 absolute unit of resistance, was a velocity. The British 

 committee adopted this unit in principle. . . . The 

 securing of a convenient unvariable resistance equal to 

 10" absolute units has been a difficult task. The B.A. 

 unit was a little too small. The 'legal ohm' was pro- 

 visionally adopted in 1883, by a committee appointed by 

 the congress of 1 88 1. It was the resistance at o' C. of a 

 column of mercury, i square millimetre in cross section 

 and ro6 centimetres long. Competent investigators, like 

 Rayleigh and Mascart, contended that this column was a 

 little too short, but some smaller values obtained by cer- 

 tain experimenters led to the adoption of the mean 

 value of 106 centimetres. The ' legal ohm ' satisfied no 

 one, and failed to become legal in any countrj'. 



" Henry A. Rowland, after pointing out errors in some of 

 the determinations previously made, found the length of 

 the mercury column in question to be io6'32 centi- 

 metres." 



As a matter of history, Rowland's paper of 1878, which 

 is not mentioned, is of much greater importance than the 

 later one, because it drew attention to the inaccuracy of 

 the original determination of the British Association. 

 There is no reason why Rowland's later investigation, 



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