Chemistry and Physics. 93 



University of Denver.) — This chart gives a survey of the most 

 important classes of organic compounds. Many structural for- 

 mulas are given, and many methods of synthesis and characteris- 

 tic reactions are included. The arrangement is systematic and 

 ingenious, and it should be useful to students in reviewing the 

 more fundamental and important facts of the subject, h. l. w. 



7. A New JT-Bay Spectrograph. — An extremely simple appara- 

 tus for photographing Rontgen-ray spectra has just been devised 

 by Matjkice de Broglie. The entire dispersing system consists 

 of a cylindrical core, about 3 cms in external diameter, around a 

 portion of which a sheet of mica is tightly wrapped. The axis of 

 the cylinder is rigidly fixed parallel to the lead slit and eccentric 

 with respect to the line of collimation of the beam of X-rays. 

 In a word, the narrow beam meets the cylindrical mica surface 

 almost tangentially. The photographic plate is placed with its 

 plane at right angles to the axis of collimation and at a suitable 

 distance beyond the cylinder. The glancing angles at the mica 

 surface of different portions of the X-ray beam increase continu- 

 ously from zero up to a certain finite limit. It follows, therefore, 

 from the well-known law of "reflection" of X-rays, that the 

 constituent radiations will be spread out as a sharply-defined spec- 

 trum on the photographic plate. If great accuracy in the deter- 

 mination of the relative positions of the spectral lines is of 

 primary importance, then the mica cylinder does not compare 

 favorably with the type of X-ray spectrograph in which a suita- 

 ble crystal is slowly rotated, for (a) the spectrum is not normal, 

 (b) both positive and negative orders of spectra do not occur, so 

 that an error in the determination of the position of the central 

 image cannot be eliminated in the usual way, (c) the dispersion is 

 less than when a plane sheet of mica is revolved, and (d) the dis- 

 persion of mica is less than that of rock salt, say in the ratio of 

 1 : 3*58. On the other hand, the apparatus involving the mica 

 cylindrical surface is rigid and incomparably simpler than the 

 apparatus requiring a rotating mechanism. The cylinder can be 

 readily used in a closed vessel susceptible of evacuation. The 

 new spectrograph records all of the spectral lines simultaneously, 

 and hence it admits of shorter times of exposure than the rotating 

 crystal system. The geometrical distribution of the lines on the 

 photographic plate is (theoretically, at least) not complicated. 

 The author calls attention to the fact that if the mica sheet were 

 given the form of a concave cylinder whose sectional generatrix 

 is an equiangular spiral, a point source situated at the pole of the 

 spiral would produce an extended source of monochromatic radia- 

 tion. The spectra reproduced in the plate are very clear and 

 sharp. — Jour, de Phys., April, 1914, p. 265. h. s. tj. 



8. The Ultra-violet Limit of the Solar Spectrum. — The results 

 obtained by Miethe and Lehmann have been confirmed and 

 extended by Albert Wigand, hence a brief account of the latest 

 investigation will be sufficient. The spectrograph used had quartz 

 lenses and crossed calcite prisms. The absorption of these prisms 



