THE POPULAR SCIENCE MONTHLY. 



ers, and termed a primer of primers. A fea- 

 ture of the work is the appending to each 

 primer of one or more extracts from current 

 electrical works on the subject matter of the 

 primer. 



In electricity and magnetism the author 

 deals with the sources and phenomena of 

 static and current electricity and magnetism. 

 His statement of the theories of magnetism 

 is a particularly clear and concise summing 

 up of the present views of the subject, and 

 it is to be regretted that he did not under- 

 take to do the same with the theories of the 

 electric current. In the primer on atmos- 

 pheric electricity our quite limited knowledge 

 of the subject is presented concisely, though 

 it is to be noted that the author follows the 

 accepted views of lightning protection, and 

 gives no hint of the recent important experi- 

 ments and theories of Prof. Lodge on this 

 subject. 



The second of the books takes its name 

 from the first three primers, which are de- 

 voted to the measurement of electric cur- 

 rents, electro-motive force and resistance, and 

 are concerned with an account of how these 

 measurements are made. 



The voltaic cell forms the subject of one 

 primer, and thermo-electric batteries of an- 

 other. The distribution of electricity by con- 

 tinuous currents and the arc and the incan- 

 descent light are considered in three primers. 

 In the primer devoted to the alternating cur- 

 rent a brief account is given of the modern 

 theory of such a current ; and in a primer on 

 alternating currents of high frequency there 

 is an excellent summary of the remarkable 

 experiments of Tesla with such currents. A 

 primer is devoted to induction coils and 

 transformers, one to dynamos, another to the 

 electric motor, and another to the electric 

 transmission of power. Other primers are 

 on electro-dynamics, electro-dynamic induc- 

 tion, and alternating current distribution. 

 The books are printed on good paper, in 

 clear type, and are of convenient size. 



ORIGINAL PAPERS ON DYNAMO MACHINERY 

 AND ALLIED SUBJECTS. By JOHN HOP- 

 KINSON, F. R. S. New York : The W. J. 

 Johnston Co., 1893. Pp.249. Price, $4. 



THE researches of Dr. Hopkinson on 

 electro-technical subjects, more especially 

 those upon the dynamo, have long been 



recognized as of the highest importance, 

 both for their theoretical interest and for 

 their value in the bearing they have upon 

 the work of the practical constructor. The 

 papers in which these researches have been 

 described have heretofore been accessible 

 only in the proceedings of scientific societies 

 and in the technical journals, and are now 

 for the first time collected in the present 

 volume. The collection consists of eleven 

 papers, five of which are devoted to the 

 dynamo, in which are developed the theory 

 and use of what has come to be known as 

 the " characteristic curve of the dynamo." 

 This curve expresses the relation between 

 the current and electro-motive force of a 

 dynamo at a given speed the horizontal dis- 

 tances or abscissas representing the amount 

 of current, and the ordinates th6 electro- 

 motive forces and in the hands of Dr. Hop- 

 kinson has been found capable of giving a 

 solution to all the complicated questions of 

 practical dynamo construction. Other papers 

 are : Some Points in Electric Lighting, the 

 Theory of Alternating Currents, the Theory 

 of the Alternate-Current Dynamos, and a re- 

 port upon the Westinghouse transformers. 

 In the first of these a very interesting me- 

 chanical illustration is given of the facts of 

 electrical induction by means of a model, 

 first suggested by the late Prof. Clerk Max- 

 well, and in the second the proper method of 

 coupling up alternating dynamos in a supply 

 circuit is pointed out, and the conditions for 

 the most efficient action determined. Alike 

 to the student and the practical dynamo de- 

 signer these papers will prove of the greatest 

 value, and will form a desirable if not essen- 

 tial addition to his technical library. 



IDLE DAYS IN PATAGONIA. By W. H. HUD- 

 SON. New York: D. Appleton & Co. 

 Pp. 256. Price, $4. 



THE author of The Naturalist in La Plata 

 gives us in this volume some further ac- 

 count of his wanderings hi South America. 

 He calls himself an "idler" here, being 

 made such by an accidental pistol-shot which 

 kept him for some time from active explora- 

 tion. Yet, though unable to go far afield, 

 Mr. Hudson gathered many curious observa- 

 tions and much store of entertaining anecdote 

 during his idle days. The reader will learn 

 from these chapters that Patagonia is not 



