REVIEWS 701 



what the student knows and how he has acquired his knowledge. This manual 

 would, generally speaking, be very suitable for students taking their second-year 

 course in electrical engineering, and the tests would give, if carried out systemati- 

 cally, not only a clear idea of the fundamental principles of direct current 

 machinery, but at the same time a grasp of ordinary commercial tests. The 

 cautions given to the students would, if observed, diminish the amount of money 

 paid by him in fines. 



The reviewer would quarrel with some of the statements which are made in 

 various parts of the book. Dogmatic statements of fact in a manual of this sort 

 should only be made where it is impossible to verify them by the outlined 

 experiments, but even when this is the case the statement, if only true in certain 

 cases, had better not be made. 



On page 2 there is the assertion " Any alternating current ammeter may be used 

 for measuring direct current," and on page 6 we are told " A Wattmeter may have 

 its range increased by shunting the current coil," and no mention is made of the 

 very rigorous conditions that the shunt has to fulfil. The student who had learnt 

 to regard text-books as infallible would get at some time a rude awakening if he 

 followed these rulings blindly. 



It is, however, a worse offence to make a statement about an experiment 

 which the tests carried out would show to be wrong, as on page 44, where we are 

 told under the heading of Theory that " The series motor is a so-called variable- 

 speed motor ; that is to say, that speed varies greatly with load when the supply 

 voltage is constant and the motor operates better at starting than the shunt motor 

 which is called a constant-speed motor." 



This statement is open to two objections : first there is the use of the word 

 " operates," the meaning of which is vague and secondly if the statement " the 

 motor operates better at starting" be taken to mean that the motor has a higher 

 starting torque than a shunt motor, it is only true when the starting current is 

 greater than the full load current as if say only half the normal current of the 

 machine is allowed to flow from the mains, the series machine will have only half 

 the starting torque of that given by a shunt motor. 



J. T. Irwin. 



An Introduction to the Study of Biology. By J. W. Kirkaldy and I. M. 

 Drummond. [Pp. vi + 259.] (Oxford : The Clarendon Press, 1909. 

 Price 6s. 6d.) 



This book would be found useful as a companion to a course of practical work in 

 elementary biology. 



It is divided into three parts: Part I. (pp. 1-39) treating of the unicellular 

 organisms — Amoeba, Saccharomyces, Sphaerella, Vorticella and Paramcecium, and 

 concluding with a chapter containing a comparative study of these and pointing 

 out their relation to various allied forms, e.g. Monocystis, desmids, diatoms, 

 bacteria, etc. Part II. (pp. 40-90) treating of simple multicellular organisms — 

 Spirogyra, Mucor, Hydra, Obelia, together with various allied forms, e.g. Vaucheria, 

 Eurotium, Fucus, Chara, Agaricus, corals, etc. Part III. (pp. 91-249) treating of 

 the higher plants and animals — earthworm, crayfish, dogfish, frog, rabbit, mosses, 

 liverworts, ferns, pine and sunflower. 



The book is illustrated with about a hundred diagrams. Of these about one- 

 fourth are apparently new, while the rest are from the works of Gcebel, Darwin, 

 Scott, Strasburger, Howes and other well-known sources, 



