344 ATMOSPHERIC ELECTRICITY. 



the same experiments in one of the courts of a larp;e building, without 

 any electrical sign appearing, which accords with the theory since 

 we know, from De 8aussure's experiments, that the electric induction 

 of the clear atmosphere is not felt in a sensible manner in places 

 inclosed on all sides. 



This last explanation indicates the true cause of the negative elec- 

 tricity of the water of cascades, since the divergence of the gold leaves 

 of an electrometer exposed to the air proves that the induction of the 

 positive electricity of the atmosphere is felt at the surface of the 

 earth, while experiment demonstrates that it is in an habitual state 

 of negative electricity. We may remark that this explanation is 

 susceptible of |.iroof of another kind ; for if it be true, tlie electricity 

 of the water of the cascades will not always have the same sign ; it 

 will be negative if the atmosphere is positive; on the contrary, it will 

 be positive when the clouds are negative. In order, then, that there 

 may remain no doubt as to the cause ot" this phenomenon, it would 

 be sufficient to examine the electricity of natural cascades in stormy 

 weather, 



Althougii the explanation of M, Belli differs sensibly from that 

 which M. Becquerel has given, yet it goes to support the cause as- 

 signed by the latter philosopher for the formation of negative clouds. 

 If the water at the moment of the evaporation is negatively electrified 

 by the influence of atmospheric electricity, the vapor must neces- 

 sarily partake of that electric state and carry away with it a portion 

 of the negative electricity. This vapor, then, in passing to the 

 vesicular state will constitute clouds negatively electrified. But, as 

 we have already observed, if the theory of M. Becquerel explains the 

 formation of negative clouds, it gives an explanation of positive 

 clouds which the present state of the science cannot allow us any 

 longer to admit, 



M. Peltier, in his new theory of the electrical phenomena of the 

 atmosphere,* considers the formation of electric clouds in a way which 

 appears more in harmony with observed facts. He remarks that the 

 atmosphere is the seat of two kinds of evaporation, one of which is 

 produced at the surface of water and of moist ground, and the other 

 at different heights in the air, when the opaque clouds pass to a state 

 of elastic vapor. The former, when the sky is serene, cannot generate 

 positive vapors, since experiment shows that when vapor is produced 

 at the ordinary temperature the electrometer exhibits no sensible trace 

 of the electricities disengaged at the instant of its formation; but as 

 this vapor is formed at the surface of the earth, which possesses a 

 great negative tension, and under the positive influence of the sky, it 

 must necessarily be charged with negative electricity. M. Peltier 

 sought to verify this by the experiment of placing the water in the 

 same conditions as it is found in nature, that is to say, under a 

 positive influence ; the vapor disengaged from water, distilled or not 

 distilled, contained in an insulated vessel and placed under a globe 

 positively electrified, was found to be negative, while the remainder 

 of the liquid remained positively electrified. 



• Comptes Eendus, torn. XII, page 307, and Annales de Chiuiie etde Physique, 3d series, 

 torn. IV, page 414, &c. 



