68 Scientific Intelligence. 



a static machine which gave a constant current. Different reflect- 

 ing surfaces were investigated. The writer refers to the discov- 

 ery of Hertz that thin metal films are penetrated by the cathode 

 rays and draws the conclusion that the corpuscles can move 

 within a metal without losing their charges. If one makes the 

 further assumption, that the corpuscles also can lose in internal 

 reflection, and that the loss of velocity of each corpuscle increases 

 with the number of collisions with the particles of the reflectors, 

 one comes to the conclusion that a strongly absorbing body like 

 platinum will give forth fewer corpuscles than a weaker absorb- 

 ing body like magnesium. The author's results seem to confirm 

 this theor}^ — Ann. der Physik, 6, 1902, pp. 81-93. j. t. 



13. Hole of Self-induction in discharges of Electricity through 

 Gases. — Various observers have shown that certain spectral lines 

 disappear when suitable self-induction is eraplo^^ed in oscillatory 

 currents. M. B. Eginitis studies the changes in heat effects pro- 

 duced in the spark terminals by varying self-induction. M. A. 

 DE Gramont believes that the proper use of self-induction may 

 lead in physical chemistry to a method of separating the spectra 

 of dissociation of metalloids. — Comptes Rendus, May 5, 1902, 

 pp. 1043, 1048. J. T. 



14. The Theory of 02:>tics ; hj VxvlT>r\jT>^. Translated from 

 the German by C. Riborg Mann and Robert A. Millikan. Pp. 

 546+xxi. New York, 1902 (Longmans, Green, and Company). — 

 Very nearly a half of the volume is devoted to a compendious 

 treatment of geometrical and physical optics, written in a clear 

 but very condensed style. The rigid deduction and application 

 of the Principle of Huyghens, founded upon the theoretical inves- 

 tigations of Kirchhoff and of Voigt, will offer the most novel 

 extensions to the familiar discussions of the current texts. 

 It is difticult to conceive how a more admirable review of 

 physical optics could be contained in so concise a form, and 

 although it can hardly be regarded as a sufficient guide to a 

 novice in this field, it is sure to give pleasure to every reader 

 who possesses the requisite elementary knowledge. 



Section II, of 220 pages, develops the electromagnetic theory 

 of light and applies it to the explanations of the enormously 

 varied optical properties of bodies. It is impossible to indicate 

 in a brief review the surprising extent of the phenomena dis- 

 cussed with- highly satisfactory completeness, or to point out 

 the vast departure in style of treatment from the best known 

 text-books on light. The last chapter of the section, however, in 

 which the theory of Lorentz regarding the modifications which 

 motion of the bodies in question introduces in optical phenomena, 

 may fairly be cited as not the least interesting. 



The final Section treats, in three chapters, of the energy of 

 radiation ; of the application of the second law of thermo- 

 dynamics to pure temperature radiation ; and of incandescent 

 vapors and gases. These are broadly philosophical and illustrate 

 the essential unity of all departments of physics. 



