362 SCIENTIFIC RECORD FOR 1884. 



that takes place when the volume occupied by the aqueous vapor is so 

 enormously diiiiiiiished as in the formation of rain drops, a view that is 

 apparently similar to that of Tait and other authorities. (Z. 0. G. il/., 

 XIX, p. 535). 



835. Prof. H. Dufour communicates to the Swiss Scientific Association 

 the results of his observations on the electricity of the air as made in 

 tbe laboratory at Lausann^^. From six months' observations with a 

 Mascart self- register, he finds a})proximately the maxima at 7 A. M. and 

 9 P. M. ; the minima between 3 and 5 p. m. and 3 and 4 A. M. Negative 

 electricity occurs frequently during very hard snow; occasionally two 

 successive precipitations separated by clearing weather sbow opposite 

 electricities. The conditions recorded by the electrometer are very 

 complicated; they depend upon the ])Otential of the air at tbe waler- 

 dropper, and on tbe induction of electrical layers on the water dropping 

 from tbe tube ; in fact, the records of the electrometer are like those of 

 a thermometer hung freely in the air whose temperature is that which 

 results from conduction to tbe neighboring air and radiation to more 

 distant objects. Dufour has attempted to separate the electric induc- 

 tion and conduction from each other as follows : The discbarge tube 

 was made to end in tbe center of a metallic cage of 40 centimeters cube, 

 each of whose six metallic sides could be removed without disturbing 

 the others. If the cage is entirely closed tbe electrometer shows the 

 potential of the mass of air streaming through it ; if one or other side 

 beremoved, tbe instrumentcomesunder the additional influence of induc- 

 tion through a definite region of space. 



Together with these observations, Dufour, by allowing drops of water 

 to fall through unelectrifled air, showed that electricnty was more evi- 

 dent in air filled with water-dust than in pure air. Clouds of smoke 

 from burning wet straw, carried iu currents of air post tbe apparatus, 

 showed for each cloud tbe presence of electricity, similarly clouds of 

 steam from a tube communicating witb the earth. If the air of a great 

 hall was electrified and strong drafts produced within^ the ball, the 

 electrometer showed variations similar to tbose recorded by tbe I'.Ias- 

 cart during the prevalence of north winds. Attempts to produce elec- 

 tricity in tbe air by tbe sudden condensation of vapor into fog gave 

 negative results. {Z. 0. G. M., xix, p. 129.) 



336. Prof. L. Palmieri publishes a little memoir summing up all bis 

 works upon atmospheric electricity. According to him tbe eloctricitj* of 

 the earth's surface is induced by that of tbe air. Tbe potential of tbe air 

 is always positive in clear sky, and so, also, during a cloudy sky, pro- 

 vided that no rain has fallen within 70 kilometers ; but as soon as rain 

 falls, positive and negative electricity rapidly alternate. Lightning can 

 only occur during or iu connection with rainfall. The origin of atmos- 

 pheric electricity is, hi- thinks, to be found in the condensation of aqueous 

 vapor. {Z. 0. G. M., xviii, p. 80.) 



337. Dr. S. Kalischer. of Berlin, has experimentally investigated the 



