592 



SCIENCE 



[N. S. A^OL. XLVII. No. 1224 



ing tendency to confine themselves to detailed 

 directions for the performance of a number of 

 more or less well selected but highly special- 

 ized electrical measurements. Such methods 

 provide an easy introduction to the technique 

 of the electrical laboratory and they are fre- 

 quently useful in dealing with elementary 

 students provided the imderlying principles 

 and their interrelations are clearly empha- 

 sized. But, when they become crystallized in 

 book form, the several experiments are apt to 

 occupy watertight compartments, between 

 which the student sees very little relation. 

 He performs the specified manipulations and 

 draws the specified conclusions without ob- 

 taining the slightest inkling of their signifi- 

 cance in electrical science, because he has been 

 relieved of the study necessary for understand- 

 ing. Moreover, owing to variations in equip- 

 ment, even the best of such books are of little 

 use except in the laboratories for which they 

 were written. 



Professor Laws's book is a welcome de- 

 parture from these methods and can not fail 

 to be greatly appreciated by serious students 

 of electrical science. It is a clear and com- 

 prehensive treatise on modern methods of 

 electrical measurement and includes sufficient 

 discussion of typical instruments to guide the 

 student in their practical application what- 

 ever may be the type of the instruments with 

 which he has to deal. A few methods of 

 purely historical interest are described, but 

 for the most part the methods and instruments 

 discussed are so thoroughly up to date that 

 many of the more recent developments can be 

 found elsewhere only in the original publi- 

 cations of their authors. Numerous refer- 

 ences to original sources direct the student to 

 first-hand discussions of the topics treated and 

 to special methods and details beyond the 

 scope of the present work. 



The following list of chapter headings gives 

 an idea of the field covered by the book: 

 Measurement of Current; The Ballistic Gal- 

 vanometer; Resistance Devices; Measurement 

 of Eesistance; Measurement of Potential 

 Difference and Electromotive Force; Power 

 Measurement ; Measurement of Inductance and 



Capacity; Induction Instruments; Electricity 

 Meters; Phase Meters; Power-factor Indica- 

 tors ; Synchroscopes and Frequency Meters ; 

 Graphic Recording and Curve Drawing In- 

 struments; Instrument Transformers; Cali- 

 bration of Instruments; Determination of 

 Wave Form; Cable Testing. 



The theory of methods and instruments is 

 logically developed from fundamental prin- 

 ciples and the conditions necessary for ac- 

 curacy are discussed at some length in con- 

 nection with practical applications. Galvan- 

 ometers of various types are treated with the 

 fulness merited by their general use as in- 

 dicating and measuring instruments. The 

 equation of motion of the suspended system 

 is developed and integrated in its general 

 form. Special cases are then derived by suit- 

 able choice of initial conditions and dy- 

 namical constants. The results thus obtained 

 are utilized throughout the book in discussing 

 the proper adjustment of resistance, control 

 torque, period, damping factors, deflecting 

 couple and sensitiveness to meet the require- 

 ments of the various uses of the galvanometer. 



The typography of the book is clear and 

 well arranged. The few misprints, inevitable 

 in a first edition, are apparent and easily cor- 

 rected. Most of the diagrams and illustrations 

 are clear and well executed but a few of the 

 halftones do not give a very clear idea of the 

 instruments represented. The reader is as- 

 sumed to be familiar with the fundamental 

 principles of direct and alternating current 

 systems of distribution and with the methods 

 of differential and integral calculus. With 

 this equipment he should find no difficulty in 

 following the author's clear and concise dis- 

 cussions. The book is well adapted for use in 

 senior college laboratories and it should also 

 find a place in the working library of every 

 electrical engineer. 



A. DEFOREST Palmer 



SPECIAL ARTICLES 



A NEW AND IMPROVED METHOD FOR OBTAIN- 

 ING PECTIN FROM FRUITS AND VEGETABLES 



For more than two years past the writers 

 have been engaged in the study of methods for 



