1 64f Mr. W. R. Birt on the connexion of Atmospheric Electricity 



opposite state ajid then attract it.^* This passage strikingly 

 illustrates the increase of the electric tension by the increase 

 of the size of the drop, nut simply by the attraction of aggre- 

 gation alone, but by the larger drops, considered as insulated 

 conductors, throwing the smaller drops into an opposite state 

 and then attracting them ; so that in addition to the attraction 

 of aggregation, by which the drops have a tendency to coalesce, 

 the electrical attraction alluded to by Howard has a tendency 

 to increase the size of the larger drops, or rather to produce 

 " an agglomeration of many minute and feebly electrified glo- 

 bules into one rain-drop." " Thus," as Howard says in the 

 passage which we have already quoted, " the drops of which 

 a cumulus consists may become larger the longer it is sus- 

 pended, and the electricity stronger from the comparative di' 

 minuiion of surface." It must, however, be understood, that 

 the larger drops thus formed are not rain-drops in the proper 

 acceptation of the term,the cumulus never affording rain unless 

 a disturbance of its electrical state takes place. 



Under the circumstances above referred to, the cumulus 

 and its particles of suspended water are regarded as charged 

 conductors bearing, not transmitting, the electric force from 

 one portion of the atmosphere to another. In this as well as 

 the other processes that have been referred to, rain does not 

 enter as a product. The remarks, however, of Mr. Howard 

 on the Jirst formation of rain are so extremely apposite, that 

 in tracing the electrical action which we are capable of recog- 

 nizing in the atmosphere, 1 shall freely avail myself of them ; 

 but as the paragraphs are rather long, I must content myself 

 with a mere reference to the pages in which they occur. 



In pages 149 and 150, vol. i. of the Climate of London, 

 Mr. Howard speaks of the first formation of rain in connexion 

 with a double mode of the formation of cloud; viz. the conden- 

 sation of vapour by refrigeration in the higher regions of the 

 atmosphere, and the production of cumuloid masses by the 

 condensation in the lower, of the vapour immediately evapo- 

 rated from the surface of the earth. In connexion with the 

 first mode, and in accordance with the former extracts, each 

 particle of cloud, each minute drop of water thus separated is 

 positively charged; and by each (thus positively charged) 

 obeying the law of gravitation, the whole subside to a region 

 in which they remain suspended, forming in that region a 

 visible haze. Now I presume, from what Mr. Howard has said 

 on the formation o^ cirrus, and his comparison of it to a. trans- 

 mitting or imperfect conductor, carrying the electric force from 

 one portion of the atmosphere to another at a great distance 

 over the intervening surface of the earth (Introduction, page 



