PHYSICS OF THE GLOBE. 159 



clonic movements of the atmosphere. He seems to conclude 

 that every time that a barometric depression is central to 

 the south of his observing station at Rouen, the sensitive pa- 

 per always turns very strongly blue. He thinks that near 

 such a depression the coloration of the paper is increased, 

 but remarkably so only on the north side, and is attributable 

 to the unequal electrization of the air. 



The showers of dust that frequently fall on ships trav- 

 ersing the Atlantic Ocean have been investigated by Hell- 

 mann, who finds that the limits of the area of dust-show- 

 ers are 6 S. and 3 N. lat., and from the coast of Africa 

 westward to 3S W. long. They are most frequent in win- 

 ter near the African coast, but in spring at points farther 

 west. The sand and dust evidently come principally from 

 Africa and the Sahara, and the coarser deposits occur in the 

 east portions of the region of dust-showers, while as we go 

 west, or away from Africa, the deposits are finer. These, 

 therefore, give us some idea of the annual change in the at- 

 mospheric currents. 



E. Yung, microscopist to the University of Geneva, com- 

 municates to La A r ature a chapter on the atmospheric dust 

 and germs collected in Switzerland. 



Miguel sends to the Paris Comptes JRendus, for June, the re- 

 sults of an investigation into atmospheric dust. His work 

 relates only to the number of corpuscles whose diameter ex- 

 ceeds two thousandths of a millimeter. He finds the average 

 number small during the winter months ; it increases rapid- 

 ly during the spring, remains stationary throughout the sum- 

 mer, and speedily declines in autumn. A fall of rain is at all 

 seasons followed by an increase sometimes a very remark- 

 able one. Temperature and moisture appear to be the con- 

 trolling;' conditions influencing; their numbers. The ova of 



CD C5 



large infusoria were comparatively rare. The spores of 

 moulds were very abundant. 



The liquefaction of oxygen, nitrogen, and hydrogen, under 

 the low temperatures and high pressures attained byPictet 

 and Cailletet, important as they are from a physical point of 

 view, can hardly be said to be of much practical importance to 

 the meteorology of our atmosphere under existing conditions. 



The work of Professor O. E. Meyer, of Breslau, "Die kinc- 

 tische Theorie der Gase," treats, in a manner as elementary 



