Chemistry and Physics. 523 



the important forms of spectroscopic apparatus supplemented by 

 the theory and practical applications of the latter. This volume, 

 as well as each of the succeeding volumes, closed with a detailed 

 index arranged with reference to authors and to subjects sepa- 

 rately. 



The second volume (1902) took up the following subjects : 

 Emission and absorption from the standpoint of Kirchhoff's law ; 

 radiation of solids ; radiation of gases ; spectra of compounds 

 and multiple spectra ; the influence of pressure, of temperature 

 and of the form of electrical discharge upon spectra ; the appear- 

 ance of spectra ; Doppler's principle ; laws of spectra ; and the 

 Zeeman effect with related phenomena. This second volume has 

 proved to be of inestimable value to spectroscopists, and it has 

 been the exciting cause of a great deal of subsequent important 

 investigation. 



The author's original intention of devoting the third volume to 

 the discussion of the phenomena of absorption and of such allied 

 matters as fluorescence, phosphorescence, and surface colors had 

 to be modified because of the enormous volume of work done 

 upon these subjects. Consequently the third volume (1905) was 

 limited to a description of the. apparatus and methods for the 

 study of absorption and to a detailed account of the absorption 

 of such organic and inorganic materials as are not derived, directly 

 at least, from the vegetable and animal kingdoms. The volume 

 in question closes with a complete list of all known absorption 

 spectra which pertain to the classes of substances just indicated. 

 If any one of the four volumes is less important than the others, 

 then it seems to be the third. 



On the contrary, the fourth volume is of fundamental impor- 

 tance not only to the spectroscopist but also to the theoretical 

 physicist, to the botanist, to the zoologist, and to the student of 

 medicine. That this is true may be seen from an inspection of the 

 following synopsis of the contents of the last published volume: 



The first chapter is devoted to a detailed account of the natural 

 coloring matters produced by plants. More specifically, the five 

 sections of this chapter deal respectively with green coloring 

 matters and their derivatives ; with yellow and other pigments of 

 leaves and flowers ; with certain coloring matters which do not 

 fall under the preceding heads ; with the colored constituents of 

 fungi, bacilli, and lichens ; and with the coloring matters of algae. 

 The second chapter deals with the coloring matters of blood, of 

 normal and pathological urine, and of bile. Animal pigments 

 are exhaustively treated in the third chapter. 



The subject matter of each of the preceding chapters is pre- 

 sented in a thoroughly systematic manner. First, the historical 

 development of each field of investigation is unfolded, then the 

 facts and appertaining opinions are discussed, and, finally, com- 

 plete lists of bibliographical references are followed by alphabet- 

 ical synopses of the characteristic absorption spectra of the sub- 

 stances concerned. Kayser expresses doubt as to the relevancy 



