THIS is a book dealing generally with electromagnets, and so far as the author records experimental results will be found useful, but the explanation of the experiments is not given as fully as is desirable in order that the reader may thoroughly understand the theoretical deductions, and the latter themselves are not always trustworthy. We find a good many quotations with due acknowledgment of articles that have appeared in the Electrical World of New York, and if the author had exercised some care in the selection his book could only have benefited by it. Unfortunately, however, the necessity of carefully probing the correctness and relevancy of any article before admitting it into his book does not seem to have occurred to the author, and the result is that we find statements in his book which often are quite useless and sometimes even unintelligible. To give only a few examples. On p. 152 is given a formula for the inductance of a solenoid for which an accuracy of half per cent, is claimed, but the author does not say whether the result is obtained in cm. or in Henry. Moreover, the formula is very cumbersome, and no proof is given. On the next page another formula is wrongly quoted from Maxwell, the exponent for the number of turns per cm. length being given as four instead of two. Also in this case the author does not state whether L is obtained in cm. or Henry. Solenoids Electromagnets and Electromagnetic Windings. By Charles R. Underbill. Pp. xix + 342. (London: Constable and Co., Ltd., 1910.) Price 8s. net.