NATURE 



[March 2, 191 1 



saw light in the pages of a Festschrift, issued by the 

 Technische Hochschule in Carlsruhe, to commemorate 

 the fifty-third birthday of the Grand Duice of Baden. 

 It does, however, contain detailed descriptions of the 

 latest forms of the microscope which have not ap- 

 peared in print before, and would, moreover, be 

 welcomed for the sake of the interesting historical 

 account of Prof. Lehmann's researches, which spares 

 the student of the subject the difficulty and trouble of 

 hunting up a series of papers published at various 

 dates and in various periodicals. 



Nearly forty years have elapsed since Prof. Leh- 

 mann, while still a student, first devised a form of 

 microscope by means of which substances could be 

 observed at higher than ordinary room temperature, 

 and the phenomenon of crystallisation watched in 

 actual operation. The results of the research thereby 

 rendered possible were, as is well known, unexpected 

 and startling, and the meaning and even the reality 

 of the observations were for long the subject of con- 

 siderable discussion and dispute. Other workers 

 have, however, in recent years entered the field, who 

 on the whole have confirmed the accuracy of Prof. 

 Lehmann's observations, and there can be no doubt 

 but that the old ideas regarding crystals and crystalli- 

 sation needed extensive modification. The investiga- 

 tions are discussed in chronological order in the 

 present book, but since we noticed them less than two 

 years ago (Nature, 1909, vol. Ixxix, p. 286), we shall 

 not recur to them here. With each step some im- 

 provement in the instrument or some additional 

 facility suggested itself until it reached the most 

 recent form, which is provided with water jackets, 

 powerful heating arrangement, means for reading the 

 temperature, and a camera, and even a kinemato- 

 graph, for giving a faithful record of the phenomena. 

 The descriptions of the different forms are elucidated 

 by excellent illustrations. 



The last chapter of the book might with advantage 

 have been omitted. Discussions of one's claim to 

 priority of discovery, and the proper appraisement of 

 one's work rarely serve a useful purpose, and are to 

 be deprecated. 



HEAT-ENGINES. 

 The Steam-Engine and other Heat-Engines. By 

 Prof. J. A. Ewing, C.B., F.R.S. Third edition, re- 

 vised and enlarged. Pp. xvii + 604. (Cambridge: 

 University Press, 1910.) Price 155. 



IN this, the third edition, Dr. Ewing has thoroughly 

 revised his well-known text-book, and to some 

 extent he has rewritten certain chapters; for ex- 

 ample, the chapter on steam turbines is new, and the 

 greater part of that devoted to gas and oil engines. 

 The most important departure, however, is that in 

 dealing with the properties of steam the author has 

 accepted the characteristic equation of Callendar along 

 with the steam tables derived from it by Mollier. The 

 old steam tables were based chiefly on Regnault's 

 well-known experiments, and it has been recognised 

 that they involve inconsistencies and errors. Prof. 

 Callendar, whose first paper on the subject was pub- 

 lished in 1900, has devised a method of treatment 

 NO. 2157, VOL. 861 





which is free from inconsistencies, and gives, whei 

 expressed in the forin of tables, results which agn 

 with all the most recent experiments, at any rate 

 between the temperatures of 0° C. and 200° C. P' 

 sibly Callendar 's equation will not give such a cl 

 approximation to experimental results for pressure 

 lying beyond the upper of these two limits of tempera 

 ture. In the form of an appendix, Dr. Ewing hai 

 added a brief account of Callendar's characteristi/ 

 equation, and of Mollier 's readjustment of the con 

 stants. Dr. Ewing has also decided to adopt tb 

 Centigrade scale throughout the whole of his b(X)k. 



In chapter v., which is devoted to entropy, thi 

 author describes Dr. MoUier's graphic methods 

 representing the properties of steam. By the aid o 

 these diagrams the engineer has placed at his disposa 

 a simple method of solving the problem of determin 

 ing the state of steam which is expanded adiabatically 

 from any initial condition whether superheated or not 

 and of determining the greatest theoretical output 

 obtainable from steam when the initial condition and 

 the lower limit of temperature are assigned. 



Chapter viii., on steam turbines, is an entirely new 

 chapter, and will be found of great assistance by all 

 engineers who are interested in the design and work- 

 ing of the steam turbine. The whole subject of the 

 design of the steam turbine is fully discussed both 

 from the theoretical and from the practical side. 



The last chapter is a new one on gas and oil 

 engines. The efficiency of the ideal cycle is worked 

 out on the assumption of constant specific heat, and 

 the author then discusses the problem of the variation 

 of specific heat with temperature, or in other words, 

 the relation between the internal energy of the gas 

 and its temperature, and discusses the effect of this 

 variation upon the efficiency of the ideal engine work- 

 ing on the ordinary gas engine cycle. 



In its present form Dr. Ewing's book will un- 

 doubtedly be the text-book most frequently consulted 

 by all engineers who have to deal with steam and 

 other forms of heat engines. T. H. B. 



GEOLOGICAL NATURE-STUDY. 

 The Earth and its Story. By Dr. A. R. Dwerryhouse. 

 Pp. 364. (London : C. H. Kelly, n.d.) Price 5.V. 

 net. 



THIS book has the same title, and covers the same 

 ground, as one issued by Prof. A. Heilprin in 

 1896. What Heilprin did for 3'oung American readers. 

 Dr. Dwerryhouse does, with even greater lucidity of 

 expression, for beginners and unprofessional natur- 

 alists in the British Isles. His book is sent out by 

 the publishers in good clear type, and is illustrated 

 by photographs and maps printed in a brown tint 

 on separate sheets of thick art paper. In this 

 respect it has an advantage over all the elementary 

 geological text-books that we know. Moreover, it is ' 

 by no means a simple text-book. It is the work of 

 a field-observer, who wishes to bring the results ob- 

 tained by geologists home to any intelligent reader. 

 Even fossil specimens are photographed, which gives 

 them, for the author's purpose, a desirable air of 

 reality, though the process will find less favour with 



