May 26, 1911] 



SCIENCE 



821 



not very clearly brought out. Tet fractional 

 pitch is very generally used in motors of 

 American manufacture. 



The chapters on the Design of Small Motors 

 for Manufacture in Large Quantities and on 

 Cost and Weight CoeiSeients are of undoubted 

 value in concentrating attention on the fac- 

 tors which govern the expense, although the 

 actual values being based on foreign practise 

 would not be of great value to an American 

 engineer. 



In a book on design as comprehensive as 

 this it seems a pity that some space is not 

 devoted to the mechanical design. It is to be 

 regretted that designers of the electrical fea- 

 tures of apparatus are so dependent on the 

 mechanical engineer to put their designs and 

 ideas into execution. 



Considerable space is given to the single- 

 phase motor both of the induction, series and 

 repulsion types, with the addition of very good 

 introduction stating the logical limitations of 

 the single-phase system. 



The author and publishers should be con- 

 gratulated on the excellent work shown in the 

 cuts and curves which contribute considerably 

 to the value of the data included in the book. 

 This is really very extensive and alone would 

 make the book of great value to the designing 

 engineer as a book of reference. 



Walter I. Slighter 



Testing of Electromagnetic Machinery. By 

 B. V. SwENsoN and B. Frankenfield. New 

 York, The Macmillan Co. 1911. 

 This volume is devoted to the testing of 

 alternating-current machinery and is a sequel 

 to the book on " Direct Current Machinery," 

 previously published by the same authors. 

 The book contains a description of a very 

 large number of practical experiments illus- 

 trating the phenomena of alternating-current 

 circuits and methods of testing commercial 

 apparatus. It is intended to be used in tech- 

 nical schools in connection with a laboratory 

 course. 



The general scheme and methods are based 

 upon the work which has been carried on in 

 the laboratory of the University of Wisconsin 

 under the authors, and contains additions and 



revisions due to the experience of Professor 

 Bryant at the University of Illinois. 



As a result of this collaboration and experi- 

 ence the text covers the field very completely 

 and the methods advocated are those that 

 would be generally conceded as the best and 

 most practical. 



The book is quite up to date both in its 

 methods and in its scope, thus a treatment of 

 the mercury are rectifier and the split-pole 

 converter are included, although the treat- 

 ment of the latter is very brief. 



It may be suggested that the experiments 

 are resolved into too elementary and simple 

 divisions and that a more efiicient use of the 

 student's time would be obtained by com- 

 bining several of the experiments into one 

 operation. There are 127 experiments listed, 

 very few of which could be omitted from a 

 good course, but these 127 could be logically 

 grouped to cover the same ground in fewer 

 operations. 



For the theoretical basis and explanation of 

 each experiment, the student is referred to a 

 very large number of references in each ex- 

 periment. The number of these references 

 will in itself tend to discourage the average 

 student to give any of them proper attention. 

 It would be of more benefit to the student if 

 a simple and concise development of the the- 

 ory were included in the text with each ex- 

 periment. However, for instructors in charge 

 of courses these references so systematically 

 arranged will be of great use. 



Walter I. Slighter 



Economic Geology, with Special Reference to 



the United States. By Heinrigh Eies, 



Ph.D. Third edition. New York, The 



Macmillan Co. 1910. Pp. xxxiv -f 589, 



pis. LVL, figs. 237. $3.50. 



The importance of geology in its relations 



with mineral resources was recognized nearly 



a century ago in the establishment of official 



surveys. Still earlier in the European schools 



of mines the formation and classification of 



ore deposits were discussed in formal courses 



of lectures. But the growing development of 



agriculture, quarrying and mining has brought 



the science of geology more and more into the 



