METEOROLOGY. 547 



X. — ELECTRICITY, MAGNETISM, AURORAS, LIGHTNING. 



Freeman has investigated the electrical state of a plate or dish trom 

 which water or other fluids is being evaporated. He finds no trace of 

 electrification, and concludes that atmospheric electricity cannot be due 

 to evaporation. 



L. J. Blake has investigated the electrified condition of the particles 

 of vapor, both condensed and uncondeused, after they ascend from the 

 evaporating dish, and finds that these also give no sign of electrifica- 

 tion, whence also it follows that atmospheric electricity cannot be due 

 to aqueous vapor. (Z. 0. G. M., xvn, p. 482.) 



Dr. Spring has attempted a more satisfactory hypothesis as to the 

 origin of atmospheric electricity, replacing the widely-prevalent view 

 according to which the atmosphere communicates its own electricity to 

 the cloud particles at the moment of their formation by condensation, so 

 that a cloud contains the total quantity of electricity that was pre- 

 viously in the corresponding atmosphere, but in a higher degree of 

 tension because of the change in condition of the aqueous vapor ; this 

 electricity now collects itself on the surface of the cloud which dis- 

 charges itself toward a similar cloud or the earth's surface like any 

 electrified conductor. Spring shows that this explanation is both un- 

 satisfactory and contradictory to well-known physical facts. Starting 

 with certain observations in the Swiss Alps, where Spring had some- 

 times found himself in the center of a thunder-storm, and had per- 

 suaded himself that a cloud does not act as a single conductor, but 

 that the individual drops or hail-stones retain the electric charge, he 

 concludes that possibly the electricity may arise partly from the ascent 

 of the moist air, partly from the friction of the falling drops, and the 

 atmosphere. The intensity of the development of electricity increases 

 with lower temperatures. Dr. Spring quotes in support of his views 

 similar observations by Osborne Keynolds in 1878 and the observations 

 made by H. Spring in 1875, which confirmed the view that the combina- 

 tion of numerous small crystals into one larger is accompanied by enor- 

 mous increase in the intensity. 



Dr. Spring made special experiments as to the possibility of elec- 

 trifying a solid body by atmospheric friction. He found a decided 

 electrification of a brass sphere produced by blowing against it a warm 

 dry current of air, the effect being somewhat proportioned to the ve- 

 locity of the current and the atmospheric pressure; he further observed 

 that rapid variations took place in the electrification of the sphere while 

 the current remained constant, as if a process of charging and dis- 

 charging were alternately going on between the current and the sphere. 

 (Z. 0. 0. if., xvii, p. 486.) 



Prof. H. von Bezold describes an electric phenomenon occurring on 

 February 19, 1882, which consisted essentially in a peculiar cloud reach- 



