Chemisi/ry and Physios. 237 



change, lines of equal inclination and equal annual change, lines 

 of equal horizontal intensity and equal annual change, lines of 

 equal vertical intensity, and lines of equal total intensity. 



II. s. u. 



8. Plane Trigonometry; by Eugene Henry Barker. Pp. 

 vii. 172, with 86 figures. Philadelphia, 1917 (P. Blakiston's 

 Son and Co.). — "The author believes that in a text-book of this 

 sort the things on which the greatest stress should be laid are 

 thorough familiarity with trigonometric functionality, acquaint- 

 ance with the interdependence of the functions, a knowledge of 

 the methods of trigonometric analysis, power of initiative in the 

 development of formulas, and a certain definite resolute skill 

 in their application to the solution of practical problems." 

 Although a final opinion of the true value of a text-book can be 

 formed only after it has been subjected to searching tests in 

 the class room, nevertheless the writer of this brief notice has 

 reached the tentative conclusion that the present volume is one 

 of the best books of its grade and scope which has come under 

 his observation for a number of years. The subject matter is 

 carefully graded, clearly presented, logically arranged, and well 

 balanced. The volume seems to contain just the right amount of 

 material for practical purposes. The diagrams are drawn in 

 bold lines, and the theorems and fundamental formulae are 

 emphasized by italic and full-faced type respectively. In 

 short, the text is characterized by appropriate contrast and per- 

 spective. The six trigonometric functions are defined as ratios 

 and the entirely unnecessary representation of these functions 

 by segments of lines associated with a circumference of unit 

 radius (so often found in elementary texts) has been completely 

 ignored. The book contains 524 examples and problems for 

 solution by the student. The volume closes with carefully 

 arranged five-place logarithmic tables and four-place tables of 

 the natural functions. 



On the other hand, the book is not entirely free from imper- 

 fections. For example, the paper is thin and very translucent 

 so that the diagrams and type show through from one page to 

 the next with annoying clearness. A few of the typographical 

 errors may be confusing to the student. On page 42, the head- 

 ing of article 29 contains, at the end, the superfluous factor 

 tan ( A + B ) . In chapter X the ' ' Exercises ' ' after the fifth are 

 numbered 5, 6, 7, and 8 instead of 6, 7, 8, and 9. Since the 

 answers to the examples in the exercises are given (pages 100 

 to 106), the slip just mentioned has led to the omission of all the 

 answers to the sixth set of the tenth chapter. h. s. u. 



9. Telegraph Practice; by John Lee. Pp. ix, 102. London, 

 1917 (Longmans, Green and Co.). — "This little book is an 

 attempt to outline the fundamentals of telegraph practice in 

 such a way as to indicate differences in method as adopted by 



Am. Jour. Sci.— Fourth Series, Vol. XLV, No. 267.— March, 1918. 

 17 



