n6 



THE POPULAR SCIENCE MONTHLY 



future. It is in this sense that we hold 

 to the doctrine of evolution. 



In our prospectus we referred to 

 the increasing number of those who 

 desire to know whither inquiry is tend- 

 ing, what old ideas are perishing, and 

 what new ones are rising into accept- 

 ance ; and we said that our periodical 

 was commenced with the intention of 

 meeting the wants of these more per- 

 fectly than any other. The editor of 

 Scribner^s refers to this as a "magnifi- 

 cent promise," and dilates upon the 

 transcendent editorial attributes re- 

 quired to realize it. To this we reply, 

 "Not if the specimen of Scribnerian sci- 

 ence we have here considered is to be 

 taken as the standard." And if we may 

 be permitted to imitate the bad exam- 

 ple of Scribner's editor, and meddle for 

 a moment with what is none of our 

 business, we should say that he had 

 better stick to his fiction and his verse- 

 making, and not deviate into that for- 

 eign field where nothing is to be gained 

 by cajoling public ignorance or cater- 

 ing to public prejudice, and where " the 

 supreme concern is, to bring thought 

 into the exactest harmony with things." 



LITERARY NOTICES. 



Spectrum Analysis in its Application to 

 Terrestrial Substances, and the Phys- 

 ical Constitution of the Heavenly 



- Bodies. By Dr. H. Schellen. D. Apple- 

 ton & Co., 1872. 



The following able notice of Dr. Schel- 

 len's book is abridged from an article in Na- 

 ture : It is not difficult to deliver interest- 

 ing lectures or to write an instructive book 

 on spectrum analysis. The rapid succession 

 of brilliant discoveries in this new branch of 

 science, the amount of fundamental facts 

 added by it to human knowledge, especially 

 in the field of the cosmical world, assure the 

 lecturer or writer, appealing to the intelli- 

 gent but not scientific public, of useful and 

 legitimate success. But what is not so easy 

 to do is, to interest at the same time the^ws 

 du monde and scientific men, by offering a 

 selection of the most recent discoveries in 



a bright and literary form attractive to the 

 former, and yet keeping for the latter the 

 appearance of precision, and exactness of 

 the numerical results. All these conditions 

 are very happily filled in " Sehellen's Spec- 

 trum Analysis," edited by Mr. W. Huggins 

 from the second German edition. 



The first part, introductory, is occupied 

 by a description of the artificial sources of 

 high degrees of heat and light, of which the 

 study is so intimately connected with the 

 chemical and astronomical phenomena em- 

 braced in the field of spectrum analysis ; 

 various apparatus, for instance, the gas- 

 burner, the magnesium lamp, the Drummond 

 lime-light, the electric spark of the induc- 

 tion coil, the Geissler's tube, and the electric 

 light produced by voltaic batteries, are de- 

 scribed, and_ the practical adjustments are 

 briefly but sufficiently referred to for a good 

 understanding of the subject. 



The second part is devoted to an ele- 

 mentary abstract of the geometrical and 

 mechanical properties of light. The fun- 

 damental analogy between light and sound 

 is developed, in order to explain to a reader 

 unlearned in optics how the color of a ray 

 is the corresponding element of the pitch of 

 a musical sound, and how it is possible to 

 define a colored ray by the time of its lumi- 

 nous vibrations. The description of refrac- 

 tion phenomena, especially the paths of 

 rays through a prism, leads naturally to the 

 separating process of the different colors on 

 which spectrum analysis is founded. 



A considerable number of chapters is 

 devoted to the construction of the simple 

 and compound spectroscope. The chief 

 points of this construction, especially the 

 contrivances for the simultaneous compari- 

 son of two spectra, the determination of the 

 position of lines in the spectrum, are care- 

 fully described. Afterward a practical ac- 

 count of the methods for exhibiting spectra 

 of terrestrial substances, for instance, me- 

 tallic salts volatilized in a gas-burner, etc., 

 will certainly interest chemists. 



An interesting chapter contains the 

 theoretical and experimental explanation of 

 the reversal of the spectra of gaseous sub- 

 stances. This phenomenon, studied inde- 

 pendently by Foucault and Angstrom, and 

 definitely generalized by Kirchhoff, is per- 

 haps the chief point of the history of spec- 



