Page:Popular Science Monthly Volume 2.djvu/128

116 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 tending, what old ideas are perishing, and what new ones are rising into acceptance; and we said that our periodical was commenced with the intention of meeting the wants of these more perfectly than any other. The editor of Scribner's refers to this as a "magnificent promise," and dilates upon the transcendent editorial attributes required to realize it. To this we reply, "Not if the specimen of Scribnerian science we have here considered is to be taken as the standard." And if we may be permitted to imitate the bad example 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 foreign field where nothing is to be gained by cajoling public ignorance or catering to public prejudice, and where "the supreme concern is, to bring thought into the exactest harmony with things."



following able notice of Dr. Schellen's book is abridged from an article in Nature: It is not difficult to deliver interesting 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 intelligent but not scientific public, of useful and legitimate success. But what is not so easy to do is, to interest at the same time gens 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 "Schellen's Spectrum 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 embraced 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 induction coil, the Geissler's tube, and the electric light produced by voltaic batteries, are described, and the practical adjustments are briefly but sufficiently referred to for a good understanding of the subject.

The second part is devoted to an elementary abstract of the geometrical and mechanical properties of light. The fundamental 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 luminous vibrations. The description of refraction 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 comparison of two spectra, the determination of the position of lines in the spectrum, are carefully described. Afterward a practical account of the methods for exhibiting spectra of terrestrial substances, for instance, metallic 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 substances. This phenomenon, studied independently by Foucault and Angstrom, and definitely generalized by Kirchhoff, is perhaps the chief point of the history of 