404 



NATURE 



[April i, 1922 



chapters to microscopic analysis, the deficiencies thus 

 left will be obvious ; to those who knew the author 

 personally, and were thus able to estimate the heavy 

 burdens which were laid on him during the anxious 

 years 1914-18, these blemishes will be regarded as 

 veritable war wounds. 



Thus, this fourth edition of a recognised standard 

 work, even with its blemishes, will be to workers in 

 the oil world an appropriate memorial to its author. 

 In most chapters there are the results of his character- 

 istically painstaking assembly of data ; the constant 

 sense of relativity shown in their summary ; the 

 judicial instinct with which conflicting theories are 

 balanced ; the conscientious recognition of the work 

 of others ; the cautious estimates of " prospects " 

 likely to affect commercial interests ; the record of 

 observations privately obtained from innumerable 

 friends ; and, finally, the signs of war weariness which 

 probably brought about the fatal illness to which he 

 succumbed only two days after passing for press the 

 complicated section on shale oil and allied industries. 



The publication of this edition marks a definite stage 

 in the history of petroleum technology ; in complexity 

 its ramifications have now passed beyond the compre- 

 hension of any one individual ; no single person can 

 hope to prepare the fifth edition of Redwood's " Trea- 

 tise." Its author has passed away, but his spirit 

 remains incarnated in the Institution of Petroleum 

 Technologists which he founded just before the war, 

 and that body might well regard as its chief mission the 

 maintenance up to date of this its bible as a standard 

 work of reference. The Institution has already in the 

 press a volume summarising recent developments in 

 special branches of the petroleum industry, and this 

 work, supplemented by Mr. Dalton's revised and 

 extended bibhography, will bridge many of the gaps 

 left in the Treatise by Sir Boverton Redwood's un- 

 expectedly sudden death. T. H. Holland. 



Entropy as a Tangible Conception. 



Entropy as a Tangible Conception : An Elementary 

 Treatise on the Physical Aspects of Heat, Entropy, 

 and Thermal Inertia for Designers, Students, and 

 Engineers, and particularly for Users of Steam and 

 Steam Charts. By Eng. Lt.-Commr. S. G. Wheeler. 

 Pp. 76. (London : Crosby Lockwood and Son, 

 1921.) 85. 6d. net. 



OPINIONS will differ as to the merits of the 

 title which Lt.-Commr. Wheeler has chosen 

 for this volume. The extreme relativist, who regards 

 the notion of force derived from our muscular sensations 

 as a relic of animism, will no doubt condemn it. 

 " To-day we have dispossessed the demons, but the 

 NO. 2735, VOL. 109] 



ghost of a muscular pull still holds the planets in 

 place." 1 On the other hand, the student of either 

 physics or engineering will welcome any suggestion 

 which assists him in understanding the nature of the 

 '* ghostly quantity," entropy. " The more shadowy 

 the conception to be visuahsed, the greater the need of 

 a definite material analogy." The quotation is from 

 the instructive presidential address to the Physical 

 Society of London delivered by Prof. Callendar in 

 191 1. Here it is pointed out that the caloric theory is 

 perfectly consistent with Carnot's principle and with 

 the mechanical theory for all reversible processtes. 

 The quantity measured in an ordinary calorimetric 

 experiment is the motive power or energy of the 

 caloric, and not the caloric itself. Prof. Callendar 

 identifies caloric with the " thermodynamic function " 

 of Rankine, or the " entropy " of Clausius. 



With this address and with the important paper by 

 Sir J. Larmor " On the Nature of Heat " (Proc. Roy. 

 Soc. vol. 94, p. 326, 1918) we imagine Lt.-Commr. 

 Wheeler is not acquainted. He sets out to give a more 

 tangible interpretation of entropy than that afforded 

 by Boltzmann's statement that it is " the logarithm of 

 the probability of a complexion." This he endeavours 

 to do, and in our opinion with considerable success, by 

 means of mechanical analogies. There is, needless to 

 say, nothing novel in such an attempt. Poynting and 

 Thomson, in their text-book on " Heat," direct 

 attention to quantities which are analogous to entropy ; 

 indeed, we may, according to Prof. Callendar, go 

 back to " the old picturesque phraseology of the 

 material fluid, implied in Carnot's waterfall." Just 

 as gravitational energy may be regarded as the product 

 of mass and the height of the mass above zero level, 

 so heat energy may be regarded as the product of 

 " thermal inertia " and temperature. Thus entropy, 

 being, as Swinburne called it, " the measure of the 

 incurred waste," may be interpreted as " incurred 

 thermal inertia." But in this book a distinct point, 

 which we had not previously met with in print, is 

 made by considering, not linear, but rotational, motion, 

 so that thermal inertia corresponds to the moment of 

 inertia, mk"^, of a rotating system. Here we have a 

 case where the rotational inertia is capable of variation 

 through changes in the value of k, the radius of 

 gyration. 



This may be illustrated by suspending a flat, 

 circular disc from a point in its circumference by a 

 thin wire by means of which it can be spun round 

 around a vertical axis (Fig. i). At first the disc will 

 rotate about its original vertical diameter, but on the 

 attainment of a certain speed the disc will start to 



1 Dr. Mott-Smith, in J. M. Bird's "•Relativity and Gravitation." 

 (Methuen, 1921.) 



