288 M. A. de la Rive on the Diwiial Variations of 



of the two electricities, which tend to unite. Sometimes the 

 winds, by mixing the air in contact with the surface of the 

 earth, and like it negative, with the positive air of the more 

 elevated regions, give rise to sheet-lightning, or to storms, 

 when there is at the same time a formation of clouds and con- 

 densation of aqueous vapours, owing to the humidity and dif- 

 ferent temperature of the strata of air which become mixed. 

 The attraction of clouds by mountains, the luminous phaeno- 

 niena exhibited at the extremity of elevated points, are like- 

 wise due to the same cause. But I will not stop to discuss 

 further all these natural and intelligible consequences of the 

 theory which I expound. I shall confine myself to one single 

 remark, which is, that we must bear in mind that in observa- 

 tions of atmospheric electricity the intensity of the electric 

 signs perceived is not always a proof of the intensity of the 

 electricity itself; for the humidity of the atmosphere, by 

 favouring the propagation of the electricity of the upper 

 strata, may give rise, as is frequently seen in winter, to 

 very powerful electrical manifestations even when the cause 

 producing them is not very powerful. The contrary is fre- 

 quently seen in summer. 



I now pass to the regular and normal mode of neutralization 

 of the two electricities. I had already suspected the existence 

 of this mode in my notice of 1836 ; but 1 did not announce it 

 positively, because there was then wanting a fact which science 

 now possesses, viz. the perfect conductibility of the terrestrial 

 globe with which the employment of the electric telegraph has 

 made us acquainted. 



To make it understood how I conceive this mode of neu- 

 tralization, I divide the atmosphere into annular strata parallel 

 with the equator; the positive electricity accumulated at the 

 external portion of this layer cannot exceed a certain degree 

 of tension without traversing rarefied and more or less humid 

 air until it reaches the polar regions, where, finding an atmo- 

 sphere saturated with humidity, it will combine readily with 

 the negative electricity accumulated on the earth. We have 

 thus the circuit formed ; each annular stratum of the atmo- 

 sphere gives rise to a current which proceeds in the elevated 

 regions from the upper portion of the stratum towards the 

 pole, redescends to the earth through the atmosphere sur- 

 rounding the poles, and returns by the surface of the globe 

 from the pole to the lower part of the stratum from which it 

 started. These currents will consequently be the more nu- 

 merous and the more concentrated the nearer we approach 

 the pole; and as they all proceed in the same direction, that 

 is to say from south to north in the upper portion of the at- 



