302 SCIENTIFIC RECORD FOR 1884. 



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

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

 apparently similar to that of Tait and other authorities. {Z. 0. 6r. il/., 

 XIX, p. 535). 



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

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

 tlie laboratory at Lausanne. From six months' observations with a 

 Mascart self-register, he finds ai)pvoximately the maxima at 7 A. M. and 

 9 p. M. ; the minima between 3 and 5 r. m. and 3 and 4 A. M. jSTegative 

 electricity occurs frequently during very hard snow; occasionally two 

 successive precipitations separated by clearing weather show opposite 

 electricities. The conditions recorded by the electrometer are very 

 complicated ; they depend upon the potential of the air at the water- 

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

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

 a thermometer linng freely in the air wbose temperature is that which 

 results from conduction to the 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 discharge tube 

 was made to end in the 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 the electrometer shows the 

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

 be removed, the iustrumentcomes under 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 electricity Avas more evi- 

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

 from burning wet straw, carried in currents of air past the apparatus, 

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

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

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

 electrometer showed variations similar to those recorded by the T.Iaig- 

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

 tricity in the air by the sudden condensation of vaj^or into fog gave 

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



338. Prof. L. Palmieri publishes a little memoir summing up all his 

 works upon atmospheric electricity. According to him the electricity of 

 the earth's surface is induced by that of the air. The potential of the 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 in connection with rainfall. The origin of atmos- 

 plierit*- electricity is, he thinks, to be found in the condensation of aqueous 

 vapor. (Z. 0. G. M., xvili, p. SO.) 



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



