402 Scientific Intelligence. 



19. Determination des Feldspaths dans les plaques minces ; par 

 A. Michel-Levy. 2d fasc, pp. 71-108, Pis. ix-xxi, (Baudry et 

 Cie.) Paris, 1 896. — The first portion of this work which has been 

 noticed in this Journal (vol. xlviii, p. 173, 1894) has already- 

 proved of great service to mineralogists and petrographers, and 

 this addition will also be found extremely useful. A new addi- 

 tional method of determination for the plagioclase series is intro- 

 duced, depending on the equal illumination [eclairement commun) 

 of zonal bands. To it is added a resume of the optical proper- 

 ties of microcline accompanied by a diagram. l. v. p. 



20. Allgemeine Krystallbesciireibung auf Grund einer verein- 

 fachten Methode des Krystalheichnens bearbeitet und mit einer 



Anleitung zur Anfertigung der Krystallnetze und Krystallmo- 

 nelle herausgegeben von Dr. Aug. Nies. Mit 182 Originalzeich- 

 dungen im Texte. 8vo. 176 pp. Stuttgart, 1895. (E. Schweizer- 

 bart'sche Verlagsbuchhandlung — E. Koch.) — The aim of the 

 author in this volume is to present the elements of descriptive crys- 

 tallography in simple form, and as developed by means of a new 

 method of drawing crystalline forms which, as he states, he has used 

 in his instruction with much success for a number of years. This 

 method is based upon the determination ot the angular points of 

 the form, projected by means of the methods of analytical geom- 

 etry, these being plotted upon sheets of paper ruled in squares 

 of 4 mm on the side. The simple mathematical relations needed are 

 explained and instructions given for the application of the method 

 described. The symbols of Naumann are employed throughout, 

 only modified to allow of the designation of each individual 

 lace. Numerous figures drawn by the author's method show its 

 practical application. 



III. Miscellaneous Scientific Intelligence. 



1. On the Diurnal Periodicity of Earthquakes ; by Charles 

 Davison, M.A., F.G.S. (Abstract received from the author.) — 

 Reference is made to the previous work of De Montessus and 

 Omori, the former endeavoring to show that the diurnal perio- 

 dicity of earthquakes is apparent rather than real, and the latter 

 pointing out that a marked diurnal periodicity characterizes the 

 aftershocks of great earthquakes in Japan. The results of 

 twenty-six registers obtained by means of continuously recording 

 instruments in Japan, the Philippine Islands, and Italy are sub- 

 jected to harmonic analysis with the following conclusions: — 



(1) The reality of the diurnal variation of earthquake-frequency 

 seems to be proved by the approximate agreement in epoch (mean 

 local time) of the first four components (24, 12, 8, and 6 hours) 

 for the whole year at Tokio and Manila, and for the winter and 

 summer halves of the year at Tokio. 



(2) In ordinary earthquakes, there is in nearly every case a 

 marked diurnal period, the maximum generally occurring between 

 10 a. m. and noon. The semi-diurnal period, though less promi- 



