380 



SCIENCE. 



[N. S. Vol. XIX. No. 479, 



translation for citing all German works by 

 their French titles. Lester F. Ward. 



Washington, D. C. 



Light Waves and Their Uses. By A. A. 

 MiCHELSON. Decennial Publications of the 

 University of Chicago. Second Series, Vol- 

 ume III. University of Chicago Press, 

 1903. 



The ' uses ' with which this book is con- 

 cerned are altogether those with which the 

 author's name is so intimately associated; that 

 is, the applications of interference methods 

 whereby light waves are made the tools and 

 units of measurements for physical and astro- 

 nomical investigation. The Michelson form 

 of interferometer, which has tremendously in- 

 creased the applicability of this method, was 

 invented as a means of attack upon one im- 

 portant problem which is here treated briefly 

 — the well-known Michelson-Morley ether-drift 

 experiment — still the subject of study, both 

 experimental and theoretical. 



An introductory chapter on wave motion 

 and the general phenomena of interference 

 serves to prepare the reader for the develop- 

 ment of the interferometer principle, by which 

 is meant the use of a plane reflecting and 

 transmitting (glass) surface to siDlit a beam 

 of light into two, which are subsequently re- 

 combined, to produce interference fringes. 

 The quantity directly measured is either a 

 movement or shift of these fringes, or a 

 change in their distinctness or 'visibility,' 

 produced by changes in the relative retarda- 

 tion of the two beams between the points of 

 separation and recombination. By this means 

 changes in the relative retardation, which may 

 in a particular case be produced by changes in 

 position of a plane reflecting surface, can be 

 measured with extreme accuracy. Again, the 

 change in relative retardation may be pro- 

 duced by changes in the index of refraction 

 of the medium through which one beam passes, 

 or motion of the medium, or by the introduc- 

 tion of transparent films — and the correspond- 

 ing shift of the fringes affords an exceedingly 

 accurate means of measuring these changes. 



Some of the many special cases in which 

 this method has been applied are dealt with in 



succeeding chapters; for example, the meas- 

 urement of angles and distances, the study of 

 spectrum lines and close groups of lines, the 

 efl:'ect of a magnetic field on light-emission, the 

 determination of the angular magnitude and 

 ' structure ' of stars, and the fundamental, but 

 less fascinating, matter of the use of light 

 waves as standards of length — i. e., the evalu- 

 ation of the meter in terms of the wave- 

 lengths of the red, green and blue radiations 

 of cadmium. 



The book is avowedly popular, being a re- 

 print of Lowell Institute lectures, and the 

 lecture style is retained throughout; neverthe- 

 less, it is to be feared that without the aid 

 of experimental demonstrations, for which the 

 good illustrations are hardly an equivalent, 

 the ' general reader ' would be rather over- 

 taxed by some of the chapters. However, 

 from the other standpoint of the preface, the 

 book as a resume in unteehnical form, of im- 

 portant researches which have occupied Pro- 

 fessor ilichelson for the past twenty years, 

 will be of great value, not only to scientists 

 who have not read the original papers, but to 

 many who have. C. E. M. 



Index to the Literature of the Spectroscope 

 (1887 to 1900, both inclusive). By Alfred 

 TucKERMAN. Smithsonian Miscellaneous 

 Collections, 1902. 



This index forms a continuation of a pre- 

 vious volume by the same author, which dealt 

 with the literature up to 1887, and continues 

 the subject up to the time when the work was 

 taken over by the International Committee for 

 Indexing Scientific Literature. The first half 

 of the book is taken up with the author index, 

 alphabetically arranged, of which the chief 

 characteristics should be accuracy and com- 

 pleteness. Concerning the former a short 

 examination sufiices to detect a fairly large 

 number of misprints, mostly trivial, besides 

 a few cases of confusion of names, and one 

 erroneous reference. Again, while absolute 

 completeness is too much to ask for, there are 

 omissions here which do not seem based on a 

 fair estimate of the relative importance of 

 various papers. 



The second half of the volume contains the 



