RECENT ADVANCES IN SCIENCE 367 



the level of the ground as well as high up. Instability is due 

 to the low temperature of the depression, which is more marked 

 high up than near the surface, but the surface temperature is 

 often below the normal. Such conditions may occur even in 

 winter. The storms are often of only moderate intensity. 



LITERATURE 



D. Brunt, A Periodogram Analysis of the Greenwich Temperature Records, 



Q. J. Royal Met. Soc, vol. xlv, 1919. 



E. H. Chapman, On the Use of the Normal Curve of Errors in Classifying 



Observations in Meteorology, Met. Office, London, Professional Note 



No. 5, 1919. 

 H. LowY, The Investigation of the Atmosphere in Cloudy or Thick Weather, 



Physik. Zs. Leipzig, vol. xx, 1919, Abstract in Set. Abs. London, vol. 



xxii. 

 Charles Marvin, Normal Temperatures : Are Irregularities in the Annual 



March of Temperature Persistent ? U.S.A. Monthly Weather Review, 



vol. xlvii, 1919. 

 J. von Hann, Uber die Theorie der Berg-und Talwinde, Met. Zeit., vol. 



xxxvi, 1919. 

 H. Jeffreys, On the Relation between Wind and Distribution of Pressure, 



Proc. Roy. Soc, vol. xcvi. Series A, 1919. 

 Lord Rayleigh, The Travelling Cyclone, Phil. Mag., vol. xxxviii, 1919- 

 Louis Besson, Diminution de la Transparence de I'air ci Paris, C. R. Acad. 



Sci., vol. clxx, 1920. 

 Andre Blondel, Sur une m^thode pour la mesure de la transparence 



atmospherique, C. R. Acad. Sci., vol. clxx, 1920. 

 A. BoNTQUiN, Meteorologie et Physique de I'atmosphere, del et terre, vol. 



XXXV, 1919, Brussels. 

 W. J. Humphreys, Factors of Climatic Control, /. Frank. Inst., Philadelphia, 



vol. clxxxviii, 1919. 

 W. Van Bemmelen, The Atmospheric Circulation above Australasia accord- 

 ing to the Pilot Balloon Observations made at Batavia, Proc. Sci. K. 



Akad. Wet., vol. xx, 19 18, Amsterdam. 

 Willis Ray Gregg, Vertical Temperature Distribution in the Lowest 5 Kilo- 

 metres of Cyclones and Anticyclones, U.S. Monthly Weather Review, 



vol. xlvii, 1919. 

 P. Garrigou Lagrange, Sur la marche diurne des elements meteorologiques, 



An. Soc. Meteor., Paris, vol. Ixiii, 1915-19. 

 C. K. M. Douglas, Optical Phenomena and the Composition of Clouds, 



/. Scot. Meteor. Soc, vol. xviii, 1919. 

 Wilhelm Schmidt, Eine Neue Schatzung des Gesamtniederschlages auf dem 



Meere, Met. Zeit., vol. xxxvi, 1919- 



F. J. W. Whipple, The Laws of Approach to the Geostrophic Wind, Q.J.R, 



Met. Soc, vol. xlvi, 1920. 



PHYSICS. By F. T. Peirce, B.Sc, Barker Graduate Scholar (Sydney). 



X-ray Reflection from Crystal Powders. — The now classical 

 researches of M. v. Laue, the Braggs and others on the scattering 

 of X-rays by crystals have, within the last few years, led to a 

 very notable extension in the substitution of a crystal powder 

 for the comparatively large, perfect crystal, hitherto considered 

 necessary. The method is a natural development, and was 



