Meteorology. oGl 



Meteorological Society, gives his views on the source of tlie elec- 

 tricity of the air about as follows : The new kinetic theory of gases 

 teaches that in a cubic inch of saturated aqueous vapor under atmos- 

 pheric pressure there are contained some three hundred trillion of par- 

 ticles. This corresponds approximately to y-Joo of a cubic iuch of water, 

 or to one rain drop of ordinary size. When eveiy particle of vapor be- 

 comes electritied for any reason, and all are at the same ])otential, then, 

 after the union of all into one rain drop, the potential of tlie latter will 

 be fifty billion times greater. From this it is evident that if from any 

 reason every particle of vapor received so slight a potential that it is im- 

 perceptible to our most delicate electrometers, yet the formation of drops 

 of water from these particles would explain the most terrible strokes of 

 lightning. Some years ago it occurred to me that the sim])le contact of 

 vapor particles with those of the air by the process of diifnsion going on 

 between them must be sufficient to produce this extremely small poten- 

 tial. Thus the source of atmospheric electricity is the contact of two 

 substances, as in Volta's apparatus, where it is the contact of two dry 

 metals. Experiments upon a small scale have not as yet confirmed this 

 view, nor can it be thoroughly investigated without making them on so 

 large a scale that i)rivate means are inadequate to cover the exj)euse. 

 {Z. 0. G. TIf., XIX, p. 301.) 



333. Prof. P. G. Tait communicates a critical summary of all suggested 

 theories as to the source of atmospheric electricity. His own contact 

 theory is given above ; the otlier theories may be briefly summarized as 

 follows: (1) Aerial friction; (2) Pouillet, combustion and evaporation; 

 (3) Saussure, vapor condensation ; (4) Peltier; and von Lamont, the per- 

 manent negative electrical charge of the earth l)y conduction and in- 

 duction electrities the air and vapor; (5) Sir William Thomson, air is 

 electritied by contact with the ground, and remains so after ascending 

 in the ordinary convection currents; (6) Becquerel, electitied corpuscles 

 travel from the sun to the earth's atmosphere; (7) Miihry, a- direct effect 

 of solar radiation; (8) Liiddens, friction of vapor against the dry air; 

 (9) The capillary surface tension of water drops; (10) The production 

 of hail-storms; (11) Friction of air against the ground or against cur- 

 rents of air. {Nature, xix, p. 517). 



334. Prof. Edlund, of Stockholm, has endeavored to determine numer- 

 ically the amount of the unipolar induction due to the relative move- 

 ments of the atmosphere and the earth considered as a magnet. The 

 measures which he has made in Stockholm give for a layer 1 meter thick 

 at the equator an electromotive force of 0.0321 Daniell's cell. Allowing 

 that the moist air is a good conductor, and that the clouds have an 

 average height of 1,000 meters, he reckons that between the earth and 

 the clouds there must exist an electro-motive force of at least 23 Dani- 

 ell's, which abundantly explains the electric tension ordinarily observed 

 in the air. The extraordinary electric tension necessary to produce a 

 lightning flash originates according to him in the increase of tension 



