136 



SCIENCE. 



[N. S. Vol. I. Ko. 5. 



of forces are passed in quick review : 1. 

 An ordinary magnetic force due to the pres- 

 ence of permanent magnetism. 2. Ordi- 

 nary electrostatic force due to the presence of 

 electrostatic charges. 3. Electromagnetic 

 force consisting of four distinct components. 

 One component is the electromagnetic ac- 

 tion of the field upon conduction currents. 

 The second component is the electromag- 

 netic action of the field upon the displace- 

 ment ciirrents. The third component cor- 

 responds to the electromagnetic action of 

 the field upon the cun-ents observed by 

 Eowland and Roentgen. The fourth type 

 of force is that between a variable current 

 and the electrical reactions set up in the 

 field by its variation. All these forces ex- 

 cept the last have been observed experi- 

 mentally. The last one is too feeble to be 

 detected by anj^ of the known experimental 

 methods. 



The work is, unfortunately, marred by 

 quite a number of typographical errors. 

 Some of them occur in the midst of important 

 and rather diificult mathematical operations 

 and will undoubtedly be a source of con- 

 siderable perplexity to the younger students 

 for whom, especially, this work is intended. 



The reviewer is of the opinion that he 

 will reecho the sentiment of every lover 

 of the Faraday-Maxwell electi-omagnetic 

 theory Avhen he states that this, the latest, 

 contribution of the brilliant Fi-ench mathe- 

 matician will be a welcome guide to every- 

 one who Mdshes to keep in close contact 

 with the latest advances of the electro- 

 magnetic theory. 



M. I. PupiN. 



Columbia College. 



The, Steam Engine and Other Heat Engines. 

 By J. A. EwiNG, Professor of Mechanism 

 and Applied Mechanics in the Universitj' 

 of Cambridge. Cambridge Universitj' 

 Press; ISTewYork, Macmillan&Co. 1894. 

 8vo., pp. xiv + 400. Price, $3.75. 

 Professor Ewing, in his article on the 



steam engine in the Encyclopaxliu Britannica, 

 gave good measure to his ability and knowl- 

 edge of the subject by the production of a^ 

 ti-eatise in which, for the first time, a system- 

 atic and fairty complete discussion was 

 attempted of the theory of the real steam 

 engine, as distinguished from the purely 

 Thermodynamic Theory of the Ideal Heat 

 Engine, which only had previously been 

 presented by writers on that wonderful 

 machine. Clark and Hirn and Iserwood 

 had cleverly shown the wide discrepancy 

 between the ideal and the real engine, and 

 Cotterill had discussed with elegance and 

 clearness the extra therm odjTiamic losses of 

 the machine ; bu^t Ewing brought together, 

 for the first time, and in such form as to 

 make his discussion useful, to theorist and 

 'practical man' and professional engineer 

 alike, in the study of existing engines and 

 in the attempt to improve upon them by 

 scientifically accurate designing and con- 

 struction. His article was a condensed, 

 biit complete, exposition to its date, of 

 scientific and practical knowledge of the 

 methods of economical production of heat 

 in the boiler, and of the economical thermo- 

 djruamic utilization of the energj^ thus made 

 available at the engine, with exact accounts 

 of the various methods of waste of thennal 

 and of dynamic energy. Had its author 

 written nothing else, this article would have 

 sufiiced to give him a full share of fame. 



His new treatise on the steam engine, now 

 issued in book form, is based upon his earlier 

 discussion, but is entirely rewi-itten to give 

 it a shape better adapted to its present pur- 

 pose, and to permit the introduction of new 

 matter. " The endeavor has been, through- 

 out, to make evident the bearing of theoiy 

 on practical issues. ' ' Some space is devoted 

 to experimental work and the discussion of 

 facts and data revealed by it. In so con- 

 densed a work it would have been impos- 

 sible to introduce as complete a study of 

 pure thermodynamics as maj' be found in 



