342 



NA TURE 



[February 13, 1902 



and Joule. If this last law, which practically amounts 

 to a definition of lieat as a dynamical quantity, coupled 

 with a statement of the principle of conservation of 

 energy, is to be admitted among the laws of motion, why 

 should the second law of thermodynamics be excluded ? 

 In chapter vii. the author discusses the possible causes 

 of loss of energy in the universe, but he might with 

 considerable advantage introduce something about the 

 degradation of available energy. This principle has an 

 important bearing on the question of the infinity of the 

 universe and the infinity of time. A finite universe can- 

 not have existed for an infinite time past, radiating its 

 energy into infinite space, but as soon as the principle 

 of degradation of available energy is assumed, a similar 

 difirculty as to infinity of time is found in dealing with 

 an infinite universe, all of whose energy ultimately tends 

 to be dissipated in the form of heat, and all of whose 

 parts tend to a common temperature. 



There is thus ample room for M. de Freycinet to write 

 a further essay on the irreversible phenomena of Nature. 

 There is another interesting field of study which he now 

 mentions only in a footnote on p. 43, namely the existence 

 of imaginary quantity and the remarkable fact that the 

 generalisation of the laws of ordinary algebra requires 

 the introduction of only one imaginary symbol. But, as 

 the author points out, in the present state of science it is 

 impossible for one man to survey our knowledge of more 

 than a limited portion of natural phenomena. M. de 

 Freycinet has given his readers much to think about in 

 the domains of infinitesimal analysis and rational 

 mechanics, and, moreover, this is written in a style which 

 makes the book easy to read. 



The Thermal Measm-eiueiit of Energy. Lectures de- 

 livered at the Philosophical ffall, Leeds, by E. H. 

 Ciriffiths, M.A., F.R.S. Pp. viii+133. (Cambridge: 

 University Press, 1901.) 

 This little book consists of an account of four lectures, 

 delivered to teachers by the author, at the request of the 

 Technical Instruction Committee of the West Riding 

 County Council. The author remarks that " The reflec- 

 tion that hundreds of such teachers should have been 

 willing to sacrifice their Saturday afternoons to the study 

 of certain physical measurements which did not even 

 possess the charm of novelty may somewhat lighten the 

 gloomy prospect sketched for us by those who hold 

 pessimistic views as to the future of Intermediate .Scien- 

 tific Education in this country." 



In attempting to render interesting a discussion of the 

 thermal measurement of energy, Mr. Crififiths undertook 

 a difficult task, which he has discharged admirably. 

 There is no trace of the " poijular lecturer" pure and 

 simple ; in his treatment of the subject success is due, 

 not to an adroit avoidance of difficulties, but to the 

 straightforward and conscientious attention given to 

 every point of importance. In the first lecture, a number 

 of well-chosen experiments are used to illustrate the 

 conversion of work into heat. The second lecture is 

 occupied with a consideration of the first and second 

 laws of thermodynamics ; incidentally the student is 

 made acquainted with some of the difficulties attending 

 thermometric determinations. In the third lecture an 

 account is given of the principal methods which have 

 been employed to determine the mechanical equivalent 

 of heat. In this connection students will welcoine the 

 description of Reynolds and Moorby's determination, 

 which has not as yet been dealt with in the text-books ; 

 it is to be regretted that more space could not be devoted 

 to this valuable piece of work. A good account is given 

 of Mr. Griffiths' own experimental test of the validity of 

 the system of electrical units. Lecture iii. closes with a 

 description of the recent experimental work of Callendar 

 and Harnes on the variation in the specific heat of water. 

 The fourth lecture possesses very great interest. .After 

 NO. 1685, VOL. 65] 



remarking that text-books frequently give the specific 

 heats of the metals to four of five decimal places, it is 

 pointed out that these results necessarily depend for 

 their accuracy on the values assumed for the specific 

 heat of water at various temperatures. (Jenerally speak- 

 ing, authors content themselves with referring to Keg- 

 nauh's results, without, however, consulting Regnault's 

 original papers. It appears that only two experiments 

 were performed by Regnaull for temperatures below 107', 

 and these were undertaken merely to test the working of 

 the apparatus used, and Regnault himself attached no 

 importance to them. As a matter of fact, Regnault 

 perfonned a series of determinations of the changes in 

 :he specific heat of water oi'cr Ihc range 107' lo 190 C. 

 After discussing the results, he stated what the nature of 

 the variation between o and 100 would be if deduced 

 by extrapolation from the experimental curve obtained at 

 he higher range. Later investigations have proved these 

 conclusions to be at fault, so that much otherwise un- 

 impeachable experimental work relating to specific heats 

 requires revision, and in many cases the data necessary 

 for this purpose are not given by the authors. 



It is finally recommended that the specific heat of 

 water between 17' and 18" C. shall be defined as of unit 

 value ; this also amounts to defining the mean specific 

 heat of water between o and 100 as of unit value. In 

 that case the most probable value of the mechanical \ 

 equivalent of heat is equal to 41S4 x 10''. E. E. 



Instruments ct Methodes de Mesures Electriques Indus- 

 triclles. By H. Armagnat. Pp. iii + 614. (Paris : C. 

 Naud.) 

 Fkw, perhaps, realise how much electrical engineering 

 owes its rapid development to the ease and precision 

 with which the measurements it needs can be made. Yet 

 it is this which renders it so amenable to mathematical 

 and scientific treatment, and it is very largely owing to 

 the fact that it can be so treated that it has progressed 

 so rapidly. The manufacture of instruments has in many 

 instances led rather than followed the development of 

 the engineering side of the electrical industry. The 

 practical engineer finds ready to his hand instruinents. 

 for almost every conceivable purpose he may require, 

 and it cannot be questioned that it is of the highest 

 importance that he should properly understand their 

 construction and limitations. M. .Armagnat's book 

 should therefore prove exceedingly useful to such men as a 

 work of reference in which they can find a full discussion 

 of the principles underlying the construction of the tools 

 they use. As the author points out in his preface, 

 beginners, and those also who habitually use instruinents, 

 are too often ignorant of their powers and of the proper 

 way of treating them. Many mistakes, often of a serious 

 nature, would be avoided if this state of affairs were 

 remedied 



M. Armagnat describes both the instruments which 

 are only to be found in electrical laboratories and 

 those which are in daily and extended commercial 

 use. It is the part of the book dealing with the com- 

 mercial instruments which will commend itself more par- 

 ticularly to the practical engineer. The author has wisely 

 confined himself to describing typical instruments of each 

 class, and has refrained from giving descriptions of the 

 numerous different examples of the type. Perhaps, how- 

 ever, an improvement would be introduced if instruments 

 of different makes were compared, as this would serve as 

 a useful guide to those who are in doubt as to what to 

 purchase most suitable for their particular requirements. 

 X'aluable information is given as to the best methods of 

 installing delicate instruments, of securing good illumina- 

 tion, freedom from vibration and outside disturbance, 

 and of carrying out observations and measurements. The 

 chapters devoted to these subjects add very greatly to 

 the usefulness of the book, especially from the point of 



