May 14. 1903] 



NATURE 



i:,'^retted that the type of lamp illustrated is not the one 



Id in this country. In other places there is an 



;)parent want of knowledge of recent progress, as, for 



X ample, where the oscillograph is spoken of as an 



instrument of little value, the point-to-point method 



being described as more practical. These, however, 



are minor blemishes, such as must be expected in a 



comprehensive work in which different branches are 



not written by separate experts. On the whole the 



book is to be commended ; the illustrations and curves 



are good and well selected. 



The last hundred pages of the volume deal with the 

 subject of photometry ; all the more important types of 

 photometer are described and illustrated, and the 

 various standards of light are carefully considered. 

 It is perhaps to be regretted that this part of the book 

 should refer more especially to gas photometry, since 

 the remainder is devoted to electric Hghting; but then 

 it is altogether somewhat surprising to find a book 

 on electric lighting forming one volume of a series on 

 chemical technology. M. S. 



Die empiristische Geschichtsauffassung David Humes, 

 mit Beriicksichtigung moderner methodologischer 

 iind erkcimtnistheoretischer Prohleme. Eine philo- 

 sophische Studie von Dr. Julius Goldstein. Pp. 57. 

 (Leipzig : Verlag der Durr'schen Buchhandlung, 

 1903.) Price 1.60 marks. 



This essay may be described as a chapter in the history 

 of applied philosophy. In Hume the author sees an 

 unique example of the philosopher applying his own 

 principles to history. In this case the experiment was 

 of little advantage to history. Hume's well-known 

 views on causation, the self, and uniformity leave 

 history destitute of any "inner essence," individuals 

 or real meaning. 



The author relieves these somewhat trite observ- 

 ations by concrete examples from Hume's " History 

 of England." Apart from these, the essay has been, 

 in the main, anticipated by Leslie Stephen's " English 

 Thought in the XVIIIth Century." Perhaps we 

 should not forget that this is a German book. Its 

 value lies solely in focusing attention on Hume as an 

 example of the way history should not be written. 

 The real value of Hume's work is hardly touched; he 

 is ranked above Voltaire, but shares with the- Enlighten- 

 ment the glory of having failed well. As to the 

 question of method, there is here only a negative con- 

 tribution. Not only has the failure of Hume and the 

 Enlightenment left chaos, but the author leaves it quite 

 an open question how history is to become a science. 

 That may be wisdom, but then the title seems dispro- 

 portionate. In the references to Green and Grose for 

 P.H. (passim) read T.H. On p. 51 (note) the refer- 

 ence is i. S. 378, &c. (not ii.). Siegwart is, of course, 

 Sigvvart (p. 11). " Aepinus " (p. 39) and the English- 

 man " Marivaud " (p. 56) are scarcely recognisable, 

 but probably symbolise " Aquinas " and " Merivale." 



G. S. B. 



Arithmetic. Part i. By H. G. Willis, M.A. Pp. 

 viii + 256 + l. (London: Rivingtons, 1903.) Price 

 15. 4d. 



This collection of examples on the simpler parts of 

 arithmetic is arranged in a convenient and workable 

 manner. The exercises are divided into thirty-nine 

 groups, each containing work enough for two or 

 three lessons; there are, moreover, duplicate sets of 

 exercises which can, if necessary, be used in alternate 

 terms. Oral questions are set at the beginning of 

 each exercise. A few examination papers, tables of \ 

 reference, and answers are given at the end of the book. < 

 The volume is likely to prove useful for junior forms. ' 



NO. 1750, VOL. 68] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can 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 communications.] 



Action of Live Things in Mechanics. 



Dr. Hobson (p. 6ii) appears to hold the view that if 

 dynamical laws are exact and irrefutable, the universe 

 must be a completely determined mechanical system, with 

 only one, and that a necessary, solution. 



I hold, on the- other hand, that though dynamical laws 

 when properly stated are perfectly true, they do not cover 

 the whole region of existence, and that, accordingly, it is 

 possible for live things to affect the motions of matter in 

 an unpredictable and capricious manner, though always in 

 accordance with the laws of motion. 



Dr. Hobson says, or implies, that they cannot so interfere 

 without destroying the complete validity or supremacy of 

 mechanical laws, and that they may as well upset the law 

 of the conservation of energy as any other. 



I reply that it is a question of fact whether they do or 

 not. Experience seems to me to prove : — 



(a) That live animals do introduce fresh considerations 

 and do disturb things — do not take the path of least re- 

 sistance, for instance ; they are actuated by all sorts of 

 non-mechanical motives, climbing the Matterhorn when 

 there is no necessity, and building structures which would 

 not otherwise be built. 



(6) That in so doing they never run counter either to the 

 conservation of energy or to any other fundamental 

 mechanical law ; they utilise the mechanical energies which 

 lie ready to their hands, directing them, but leaving their 

 amount unaltered. 



[I emphasise the energy aspect because I so often find 

 philosophers assume that any interference of life with in- 

 animate matter must contradict the conservation of energy^ 

 or else must involve the doctrine that life itself is a form 

 of energy.] 



I ask Dr. Hobson to admit that a unique solution of all 

 future material motions is only possible in a problem fron> 

 which all other aspects of the universe have been abstracted, 

 so that we limit ourselves by hypothesis to a purely 

 dynamical system. 



There are many things in the universe beside mechanics, 

 some of which, by odd chance, are enumerated in a footnote 

 accidentally occurring below Dr. Hobson's letter. For 

 simplicity it is customary to eliminate all these from 

 dynamical problems. But the questions at issue are : — 



(i) Whether any of these things can interact with or 

 influence a dynamical system at all. 



(2) Whether they can so interact without upsetting or 

 contradicting any fundamental dynamical laws. 



I wish to answer both these questions in the affirmative. 

 But it must be understood that by " dynamical laws " I 

 mean the fundamental ones — let us say those of Newton. 

 I do not mean modern generalisations or comprehensive 

 summaries, like the principle of Least Action, the applica- 

 bility of which can only be postulated on certain simplifying 

 assumptions — assumptions or abstractions which, in the 

 present instance, merely beg the question in dispute. 



If Dr. Hobson does not agree with this, I trust he wilt 

 give us the benefit of his further criticism. 



May 2. Oliver Lodge. 



The Glorification of Energy. 



Prof. Tait, whenever he wrote of the principle of the 

 conservation of energy, almost invariably spoke of it as 

 the "grand" principle of conservation of energy; and, 

 following his lead, all but the most sober mathematicians 

 use the laudatory adjective when they write about this 

 particular physical principle. 



It may not be altogether superfluous to point out that 

 there are other principles equally entitled to the epithet 

 " grand." For example, there is the " grand " principle 

 of the conservation of matter; .there is the " grand " prin- 

 ciple of the conservation of force, the sum total (algebraic) 

 of which in the universe is zero, according to Newton's 



