464 Scientific Intelligence. 



18. Loss of electrical charges in air which is traversed by ultra- 

 violet rays. — P. Lenard published a paper on the effect of ultra- 

 violet rays on gas in the Annalen der Physik, No. 1, 1900, p. 486. 

 He now continues his investigation and shows that the effect of 

 ultra-violet light is fourfold. The air is divided into bearers of 

 negative electricity which appear to be charged atoms or mole- 

 cules; bearers of positive electricity of larger dimensions; nuclei 

 of vapor which are non-electrified ; and ozone. — Ann. der Physik, 

 No. 10, 1900, pp. 298-319. j. t. 



19. Handbuch der /Spectroscopic von H. Katser. Erster Band. 

 Pp. xxiv, 781; large 8vo ; 781 figures in the text. Leipzig, 1900 

 (S. Hirzel). — The preparation of a comprehensive work on a sub- 

 ject which has had so remarkable a development as that of spec- 

 troscopy in its different branches, is a labor of such magnitude 

 that we may well honor the energy of the author who ventures 

 to undertake it. But here we have not simply the promise but 

 also its fulfilment in the completion of a considerable part of the 

 undertaking. The present volume of nearly eight hundred pages 

 by Professor Kayser, is so thorough and so satisfactory a treat- 

 ment of the portions of the subject here included, that the reader 

 feels justified in looking forward with confidence to the comple- 

 tion of the remaining tour volumes promised as a well-rounded 

 whole. 



The volume opens with an admirable summary, scientific and 

 yet thoroughly readable, of the history of spectroscopy from the 

 time of Newton down to the present. Although an exhaustive 

 treatment of this subject might well extend the chapter to the 

 limits of a volume by itself, the author presents the salient points 

 in the successive steps of progress, and the contributions of each 

 worker so clearly, that the chapter as a whole leaves little to be 

 desired. In the treatment of the delicate question of the claims 

 of earlier writers to the discoveries which are usually connected 

 with the name of some physicist who has come later, the author 

 shows much discrimination and critical care ; for example in 

 regard to the relative amount of credit to be given to Wollaston 

 as contrasted with Fraunhofer, or to Talbot, Miller and Stokes as 

 compared with Kirchhoff. The same critical method appears 

 throughout. The five other chapters of the volume deal with 

 the practical working of spectroscopy. The first of these dis- 

 cusses the production of incandescent vapors in the flame, arc- 

 light, or vacuum tubes. This subject is treated both historically 

 with a multitude of references to original authorities and descrip- 

 tively as needed by a present worker. The two chapters follow- 

 ing discuss prisms and diffraction gratings, giving the theory, 

 construction and use in detail. In the former subject the author 

 has been aided by Dr. H. Konen, while Prof. C. Runge has 

 furnished for the volume his theory of concave gratings. The 

 concluding chapters are devoted to spectroscopic apparatus and 

 measurements, the use of photography and other methods. Here, 

 as throughout the volume, we are struck with the simplicity and 



