430 



NA TURE 



[March 8, 1894 



the medium, at others less, than is accounted for by the 

 increase in electrokinetic energy, and that similarly 

 when energy is being returned from the medium more or 

 less is received than disappears from the electrokinetic 

 energy of the field. It seems not impossible that these 

 energy differences may be related to the cyclic changes of 

 dimensions of a specimen of iron, which it has been shown 

 recently by Mr. Nagaoka {Phil. Mag. Jan. 1894) ac- 

 company the cycles of magnetisation. 



In chapter iv. we have a business-like discussion of 

 what the author calls the establishment of electric 

 pressures, in which the building up of a nearly uniform 

 current by the commutation of successive sinusoidal 

 currents in the different sections of the armature is 

 descrioed in the usual manner, but clearly and without un- 

 due elaboration. The winding of Gramme and Siemens 

 armatures is dealt with in the same chapter, which ends 

 with some numerical calculations of armature constants, 

 and the heating caused by the Joulean dissipation of 

 energy in the coils. 



Hopkinson's method of studying dynamo construction 

 by means of the idea of the magnetic circuit, in con- 

 junction with his brilliant invention of dynamo character- 

 istic curves, and the valuable practical results which he 

 and others have obtained by this mode of investigation, 

 have gone far to clear up the whole subject of the design- 

 ing of steady-current machines. Prof. Jackson has done 

 well to devote a considerable amount of space to this 

 part of the subject ; in fact, taking in the topics of 

 regulation and connecting dynamos, it occupies no less 

 than half the present volume. Opinions will no doubt 

 differ as to the practical value of a good deal in this 

 chapter, but the selection made seems satisfactorily 

 dealt with. 



Short chapters on efficiencies and multipolar dynamos 

 conclude the volume. A second is promised on alter- 

 nating current and arc lighting machinery. 



As it is the object of the author only to present funda- 

 mental principles, and he very rightly holds that the 

 electrical student should study typical dynamos mainly in 

 the workshop or generating station, he has not burdened 

 his pages with cuts of actual machines of different kinds. 

 There the student who has had a sound course of instruc- 

 tion such as this book represents, based upon previous 

 knowledge of certain cognate subjects, and satisfactory 

 divergences into others, will be able to read to advan- 

 tage what is essential of the more elaborate works of 

 reference on dynamo machinery. 



A small incidental advantage is the absence of those 

 embarrassing folding plates, which cannot be avoided in 

 works of the latter kind, and which, instead of being 

 printed on cloth-backed sheets, arranged to fold always 

 at the same place, are made of the most exasperatingly 

 brittle and frail material. 



The book is excellently printed in good, bold type, and 

 reflects credit on the Norwood Press, Boston. There is 

 less than we have seen in some other cases of that dis- 

 agreeable glare of regularly reflected light from the hot- 

 pressed paper, which renders many American books, 

 notwithstanding their often excellent typography, so 

 difficult to read with comfort. 



A. Gray. 

 NO. I 27 I, VOL. 49] 



INTERNAL COMBUSTION MOTORS. 



A Text-Book on Gas, Oil, and Air Engi?tes. By Bryan 

 Donkin, Jun., M.Inst.C.E. (London: Charles Griffin 

 and Co., Ltd., 1894.) 



AS the results of recent researches on internal com- 

 bustion motors are usually only to be found in the 

 proceedings of our technical societies and institutions, 

 we greet the present volume with pleasure. The gas 

 engine in its present form has attained a lasting 

 success, and this is due principally to the labours 

 of Messrs. Crossley Bros., of Manchester, a history 

 of that firm being really a record of the advance 

 of the gas engine from its early stages to its present high 

 state of development. The manifold advantages of a gas 

 engine over a steam engine are evident, particularly when 

 the power is required intermittently ; moreover, for elec- 

 tric lighting, this type of motor is invaluable for small 

 powers, being started at a few minutes' notice. For 

 larger powers where town gas would be expensive, the 

 addition of a Dawson gas plant renders it far more econom- 

 ical in fuel consumption than any steam engine, and with 

 proper supervision the cost of repairs can be maintained 

 at a low figure. Once started, a gas engine can be 

 allowed to run for several hours unattended, thus reduc- 

 ing the cost of skilled attention to a minimum. 



Experiments are now in progress with the object of 

 reducing the consumption of gas in the Crossley Otto 

 engine, and the following results show the progress made 

 in this direction. A 14-h.p. nominal engine has recently 

 been tested, and gave a brake horse-power of 3991, and 

 used i6"487 cubic of gas per b.h.p. per hour. These 

 results are far in advance of the older engines, and show 

 there are still means of improving what is already a 

 wonderfully economical motor. 



Mr. Donkin's work is divided into three parts, treating 

 respectively of gas, air, and oil engines. Part i., on gas 

 engines, is divided into two sections, the first dealing with 

 the early history of these motors, and the second with 

 I modern gas engines. The subject of gas engines occu- 

 pies more than half the book, and has been treated in a 

 careful and very complete manner ; most known engines 

 are described and illustrated, and indicator diagrams are 

 shown in many cases, thus rendering the descriptions 

 very complete. Although the Atkinson engine has not 

 come in for very general use, it is an excellent example 

 of a type giving an impulse every revolution, using one 

 cylinder, whereas the Crossley engine gives an impulse 

 every two revolutions. Another engine of a similar type 

 is that designed by Prof. Rowden, and although it is not 

 described in this work, or elsewhere, yet the consumption 

 of gas is very low per brake horse-power, and owing to the 

 complete expansion of the heated gases the water jacket 

 round the cylinder is not so necessary. 



Part ii. of the volume under review deals with petroleum 

 engines, a class of motor now rapidly coming to the front, 

 and used in places where gas is not available. If Messrs. 

 Crossley Bros, can claim the honour of having made the 

 gas engine a practical working success, Messrs. Priestman 

 can claim the same honourable position as regards the 

 oil engine. Like all new machines it is more or less 

 complicated, and recent engines made by other firms 



