2 



SCIENCE 



[N. S. Vol. XXV. No. 627 



he helped to discover can be considered 

 more unexpected or more inexplicable than 

 the death of Professor Pierre Curie. 



The manner in -which the clew given by 

 uranium rays was taken up and followed 

 out with persistent endeavor, clearness of 

 vision, simplicity of life and modesty of 

 character, has been rarely paralleled in the 

 history of physics. 



Our admiration for his scholarship and 

 for his generous chivalric nature is united 

 with a keen sense of loss to science and a 

 warm sympathy for his brilliant and loyal 

 comrade. 



On the fifth of July, last, Germany and 

 the rest of the world suffered a deplorable 

 and inexplicable loss in the death of Pro- 

 fessor Paul Drude. Brilliant and numer- 

 ous as his achievements were, it is difficult 

 to believe that his work was more than half 

 done. Perhaps no better illustration of his 

 genius can be found than in the beautiful 

 manner in which he has quantitatively con- 

 nected the subjects of thermal and electric 

 conductions, on the basis of the electron 

 theory; while his two splendid volumes 

 have rendered all students of physics his 

 debtors. 



The death of Boltzmann, two months 

 later, was an equally great mystery. The 

 most valuable work of this remarkable and 

 somewhat bizarre character undoubtedly 

 lies in the field of the kinetic theory of gases. 



His treatise on this subject constitutes 

 for me— I confess it freely, but sadly — 

 a sealed volume. Were I to attempt to 

 convey to you any idea of its importance 

 I should feel, only in a much truer sense, 

 what Boltzmann himself expresses in the 

 preface of his wonderfully lucid exposition 

 of Maxwell's electromagnetic theory, when 

 he quotes from 'Faust.' 



" So soil ich deim mit saurem Schweiss, 

 Euch lehren was ich sclbst nicht weiss." 



Boltzmann 's two visits to America, one in 



1898 and one in 1904, were full of interest 

 for many of the members of this section. 

 Suffice it to say that some of his colleagues 

 have expressed the opinion that since the 

 death of Helmholtz, Boltzmann has been 

 the leading physicist of Germany. 



I beg now to call your attention to a 

 matter which seems to me somewhat inti- 

 mately connected with spectroscopic prog- 

 ress. And one can perhaps do this most 

 simply by first offering a definition of 

 spectroscopy; secondly, stating what may 

 be considered the fundamental facts of the 

 science; and, thirdly, considering to what 

 extent these facts— for one hesitates even 

 yet to call them 'principles' — are explained 

 by any general theory of the subject. 



Any explanation of light which is gen- 

 eral and satisfactory may be said to in- 

 clude at least two chapters, namely, one 

 which shall explain the transmission of 

 radiation and another which shall treat of 

 the origin or production of radiation. The 

 first chapter treats of the electromagnetic 

 ether ; the second treats of matter which is 

 at once 'the source and recipient of radia- 

 tion. ' 



It was in the autumn of 1888 that the 

 experiments of Hertz in a certain sense 

 closed the chapter on the transmission of 

 light, a large part of which had been writ- 

 ten by Maxwell in 1864. Since then, the 

 second portion of the theory— that dealing 

 with the radiant atom— has assumed larger 

 importance. Any treatment of the pro- 

 duction of radiation falls more or less nat- 

 urally into three parts, namely, (1) the 

 radiation of solid and liquid bodies which 

 is almost, but not quite, independent of 

 atomic structure; (2) the radiation which 

 takes its rise in radioactive substances and 

 which is apparently dependent upon atomic 

 collapse; and (3) the radiation of gaseous 

 substances, dependent almost entirely upon 

 normal atomic structure, and possibly also 

 upon the mode of excitation. 



