820 



SCIENCE 



[N. S. Vol. XL. No. 1040 



reducing the fundamental equation to its 

 simplest form F = ma. The author points out 

 also that it is possible to vary the procedure 

 by choosing arbitrarily the unit force and 

 adopting a kinetic definition of the unit mass ; 

 and he uses the word " slug " to designate the 

 mass to which the pound-force would give an 

 acceleration of 1 ft./sec''. His explanation of 

 this matter seems to the writer to be entirely 

 sound, as well as being an aid to the student 

 in acquiring a clear understanding of the 

 fundamental law. 



The entire treatment of force and of the 

 laws of motion is notably free from the vague- 

 ness which too often characterizes the expo- 

 sition found in text-books. The words push 

 and pull are freely used, and the fact is ex- 

 plicitly stated at the outset that every force 

 is exerted hy one body upon another body. 

 The law of action and reaction is stated in 

 the following words : " When one particle 

 exerts a force upon another, then the latter 

 exerts one upon the former; and the two 

 forces are equal, colinear and opposite." 

 Most of the difficulty that arises over this law 

 is due to losing sight of some one or more of 

 the facts that are here explicitly stated. If 

 it is kept clearly in mind that an action and 

 its reaction (a) always concern two bodies 

 and only two and (b) never act upon the same 

 body, there is little difficulty in avoiding the 

 confusion that is often associated with such 

 terms as " inertia-force " and " kinetic reac- 

 tion." L. M. HosKiNs 



Stanford TJnivbrsitt 



Principles of Electrical Measurements. By 

 Arthur Whitmoee Smith. New York: 

 The McGraw-Hill Book Company, 1914. 

 Pp. xiv + 343. 



In a laboratory course, emphasis may be laid 

 by one teacher on manipulation and details of 

 apparatus and, by another, on the principles 

 underlying the methods employed in making 

 the measurements. Professor Smith does the 

 latter and has developed a text that is suitable 

 for classroom as well as laboratory. The book 

 is written for the instruction of those who are 

 beginning their course in electrical engineer- 



ing or who desire a more complete understand- 

 ing than is afforded in most elementary man- 

 uals. It shows thoroughness and care in its 

 preparation. In addition to a discussion of 

 subject-matter usual in a laboratory manual of 

 this kind — as ammeter and voltmeter methods ; 

 use of the galvanometer, bridge and potenti- 

 ometer; measurement of current, power, capac- 

 ity and inductance ; magnetic tests of iron and 

 steel — the author includes chapters on electro- 

 magnetic induction, on the definition of the 

 Maxwell and on alternating currents, which, 

 while not essential for one only interested in 

 the taking of readings, lead the student to a 

 better understanding of the subject as a whole. 

 Frederick Bedell 



A Manual of Bacteriology for Agricultural 

 and Science Students. By Howard S. Eead. 

 Ginn & Co. $1.25. 



This little manual of 179 pages contains a 

 collection of experiments, descriptions of 

 methods, formulae for media and reagents, and 

 other information of practical use in a bac- 

 teriological laboratory. It is intended as an 

 outline of a course for students, but it would 

 be quite difficult, indeed, practically impossible, 

 in an ordinary laboratory, for a student to 

 follow this course consecutively, since the ex- 

 periments described follow each other in an 

 order that, while logical for study, would be 

 almost impractical to carry out in a laboratory 

 class. As a result the student can not follow 

 the course without very careful thought and 

 selection of experiments on the part of the 

 teacher. The book is therefore more valuable 

 for a manual for reference than as a distinct 

 course for students to follow. It contains 

 large numbers of experiments, and if properly 

 used can be made of great use as a foundation 

 of a course in bacteriology. It is more com- 

 plete, more up-to-date, and contains more of 

 the recent additions to bacteriological meth- 

 ods than the other manuals which have been 

 published in the last few years. It is made 

 more valuable by having in addition to meth- 

 ods strictly bacteriological some which are 

 especially designed for the study of yeasts, 

 and of common molds. While the methods are 



