February 25, 1909] 



NA TURE 



485 



whicli Ifad 10 the calculation of the efficiency of re- 

 frigerating engines. 



Starting with the conception of a refrigerating 

 engine as a heat pump which requires the expenditure 

 of mechanical energy to bring heat from a lower to 

 a higher level of temperature working on a reversed 

 Carnot's cycle, the significance of indicator and 

 entropy diagrams is explained in non-mathematical 

 language. The thermodynamical details are worked 

 out more completely in various appendices. These 

 include discussions of entropy (#) diagrams, with either 

 temperature or thermodynamic potential (/) as the 

 other coordinate. .\ reproduction on a large scale of 

 Dr. R. Mollier's <^-i diagram for carbon dioxide is 

 given at the end of the book, and its usefulness in 

 tracing the exact behaviour of an engine using this 

 as working substance is shown. There are also tables 

 of the properties of ammonia, sulphur dioxide, carbon 

 dioxide, and water vapour which would be necessary 

 in such calculations. .\11 these data are given in 

 C.G.S. units, and it is to be regretted that these have 

 not been used throughout the book so as to make it 

 more uniform, and also because there is a strong 

 opinion now that either C.G.S. or some derived units 

 founded on them would be used internationally in 

 applied thermodynamics with the same advantage as 

 they have been in applied electricity. 



.Absorption and air-compression machines are now 

 only employed in special cases, but they are interesting, 

 and arc considered in the second and third chapters. 



.At the present time, nearly all new installations use 

 the vapour-compression system to which the fourth 

 chapter is devoted. The substances which are used 

 are water vapour, which is clearly only applicable in 

 very special cases, carbon dioxide, sulphur dioxide, 

 ammonia, and methyl chloride. Each of these has 

 special applications, determined by size or danger of 

 explosion, or the unwholesome nature of the gas, in 

 addition to their efficiencies as working substances. 

 It is shown that the theoretical efficiencies increpse 

 in the order given with the exception of the last, 

 which is only just mentioned, although it is employed 

 in well-known cascade installations, and is coming 

 into use largely as a convenient substance for small 

 portable machines on rail-road cars and similar places. 

 This chapter, in connection with the following sections 

 devoted to the testing of refrigerating machines, es- 

 pecially by the Munich method, should be of consider- 

 able use to students and other w-orkers in this field. 

 Short accounts follow of the principal applications of 

 moderate cold in industries such as brewing and 

 others depending on fermentation processes, also in 

 ice-making, and in the preservation and transport of 

 food and other perishable articles. A section is devoted 

 to the cooling of magazines in ships of war, about 

 which the author writes with special authoritv. 



The remainder of the book discusses the production 

 and application of very low temperatures, such as 

 those obtained by liquid air, liquid hydrogen, and now 

 quite recently by liquid helium. There are three 

 principal methods of reaching these low temperatures, 

 which are all described : the cascade of Cailletet and 

 Pictet, the expansion method of Siemens and others, 

 N'O. 2052, VOL. 79] 



and the combination of the cooling due to throttling 

 and the regenerative principle by Linde. The main 

 industrial application is for the production of oxygen 

 from liquid air, which is obtained by the Linde process 

 or by the modification of this introduced by Claude, in 

 which the Siemens principle is combined with it. 

 There are considered in detail, and it is shown how 

 the rectification is carried out so that nearly pure 

 nitrogen, as well as nearly pure oxygen, is obtained 

 bv the same process. De war's work on hydrogen 

 follows, with a resume of its properties and a mention 

 of those of liquid helium. 



The book is well illustrated with diagrams and 

 drawings, and has a good index. F. H. 



OUR BOOK SHELF. 



Priiuiples and Methods of Physical Education and 



Hygiene. By W. P. W'elpton. Pp. xix + 40i. 



(Cambridge: University Tutorial Press, Ltd., 1908.) 



Price 4^. 6rf. 

 This book is addressed to the teachers of elementary 

 schools, and to such of them as enjoy the study of 

 phvsiologv much pleasure will be derived from the 

 perusal of every chapter. The author, we see, is 

 master of method in the L'niversity of Leeds; he 

 describes methods as well as theory of cleanliness, 

 ventilation, care of the eye, and such " first aid " 

 as is likely to be called for. More theory than method, 

 however, is set down to advance the practising of the 

 physical exercise part of physical education. \\'e have 

 no' idea how the author would arrange to get the best 

 use out of the school playground ; how he would 

 attain some organisation of games among scholars 

 without encroaching upon the teacher's time. 



" Glvcogen " is referred to seven times in the 

 index, but one can find no list of games or activities 

 that suit the different periods of school life, such as 

 would be helpful to the organiser of physical educa- 

 tion ; accordingly one regrets that theory dominates 

 this work. We are apt to forget that our professional 

 trainers of athletes have been very successful in their 

 way, and with them athletics called the trainers into 

 being ; a development of play is the first step towards 

 bettering physical education. 



Evervone interested either in games or physical 

 education in its fuller aspect will be delighted with 

 the chapter on the history of physical education, con- 

 tributed by Prof. J. Welton, with quotations such as 

 that troni Lucian on the Athenian boy. " When he 

 has laboured diligently at intellectual studies and his 

 mind is sated with the benefits of the school curri- 

 culum, he exercises his body in liberal pursuits, riding 

 or hurling the javelin or spear. Then the wrestling 

 school with its sleek oiled pupils labours under the 

 midday sun, and sweats in the regular athletic con- 

 terits. Then a bath, not too prolonged; then a meal, 

 not too large, in view of afternoon school. For the 

 schoolmasters are waiting for him again, and the 

 books which openly or by allegory teach him who 

 was a great hero, who was a lover of justice and 

 puritv. With the contemplation of such virtues he 

 waters the garden of his young soul, ^^'hen evening 

 sets a limit to his work, lie pays the necessary tribute 

 to his stomach and retires to rest to sleep sweetly 

 after his busy day." Education in this breadth and 

 spirit, lost in the dark ages — for the exercises of 

 chivalry do not represent it — was revived in Italy at 

 the Renaissance, and the first English exponents of 

 this revival — Mulcaster, 1581, and .Sir Thos. Elyot, 

 ijji — had their influence dominated by the Puritanism 



