552 



SCIENCE. 



[N. S. Vol. XXIV. No. 618. 



the sum of the squares of the residuals is di- 

 minished by this process, it is taken as a proof 

 by the average computer that the introduction 

 of the new unknown represents a closer ap- 

 proximation to the truth. As a matter of 

 fact it is easily shown that the new unknown 

 will always reduce the sum of the squares of 

 the residuals, and consequently these dimin- 

 ished numbers are no proof of greater ac- 

 curacy. 



It is with the spirit of caution born of long 

 practise that Wright and Hayford approach 

 the subject. In the preface of the present 

 volume, which is a second edition of Wright's 

 ' Treatise on the Adjustment of Observations,' 

 Mr. Wright tells us that so much of the new 

 work is from Mr. Hayford's hands that it is 

 no more than right that his name appear on 

 the title page. The first edition is a very 

 excellent book and has for years been recog- 

 nized as the practical standard. The second 

 edition is, if possible, better than the first, for 

 it adds the great experience that Mr. Hayford 

 has had in the work of the United States Coast 

 and Geodetic Survey as chief of the Compu- 

 ting Division. 



This experience is shown in chapter IX., 

 wherein the principles of least squares are ap- 

 plied to a very important but little employed 

 use, namely, that of the selection of methods 

 of observations, for it may be possible for 

 the observer either to increase the accuracy 

 of his work by different instrumental methods 

 or, on the other hand, to attain a given stand- 

 ard of excellency by a smaller amount of 

 observing. The suggestions for applications 

 to latitude and longitude determinations, the 

 student of geodesy will find very helpful in- 

 deed. 



The great advance in geodetic work during 

 the past quarter of a century will be seen by 

 referring to p. 349 of the first edition (pub- 

 lished in 1884), wherein it says that, 



During the present century two forms of ap- 

 paratus have been used in the measurement of 

 primary bases, the compensation bars, and the 

 metallic-thermometer apparatus. * * * Indica- 

 tions are not wanting that both forms will be 

 supplanted before long by an apparatus consisting 

 of simply a single metallic bar. 



Since this was written the iced-bar and 

 steel tape have made great changes in geodetic 

 work. 



The method of least squares which derived 

 its birth from Legendre's attempt to find the 

 figure of the earth thus receives a notable ad- 

 dition by its application to present geodetic 

 problems. 



S. A. Mitchell. 



TechniTc des physilcaUschen Unterrichts. Von 



Freidrich C. G. Miller. Berlin, Otto 



Salle. 1906. 



This volume of 364 pages is, as its title sug- 

 gests, designed for the assistance of the in- 

 structor who must give a series of experi- 

 mental demonstrations before a class begin- 

 ning the study of physics. As is indicated 

 by the preface, and also by the subject matter 

 of the book, the class of students for whom 

 the lectures have been especially designed 

 would correspond in this country to college 

 students in their first or second years. 



The work is divided into thirteen parts: 

 General Arrangements for Physical or Chem- 

 ical Instruction, Measurements and Weighing, 

 Statics, Dynamics, Statics and Dynamics of 

 Liquids, Statics and Dynamics of Gases, 

 Acoustics, Heat, Optics, Mag-netism, Electro- 

 statics, Electrodynamics, Introduction to 

 Chemistry. Under each of these heads vari- 

 ous important experiments are described in 

 detail, and nothing could be clearer than the 

 directions and suggestions. The author em- 

 phasizes at every point the necessity of the 

 demonstrations being made in a quantitative 

 manner, and he indicates the most suitable 

 means by which measurements of all kinds 

 can be made in such a manner as both to be 

 accurate and to be visible to a comparatively 

 large audience. 



The book is by far the best of its kind that 

 has come to the attention of the reviewer. 

 It is not exhaustive, it is true, nor is it ex- 

 hausting in its details. It should prove of 

 value to every lecturer in physics and chem- 

 istry who has to deal with elementary classes. 



J. S. Ames. 



