1 66 Mr. W. R. Birt o?i the connexion of Atmospheric Electricity 



produced under such circumstances. In either case, whether 

 it be a direct formation of cirrostratus from haze, or a second- 

 ary formation of this cloud from cirrus, the more perfect in- 

 sulation of the charged aqueous particles which obtains in the 

 cases of cumulus and cirrocumulus is not present. In fact 

 the cirrostratus is a cloud more or less prevalent in a moist 

 state of the atmosphere ; and in contrasting its formation from 

 cirrus with the formation of cirrocumulus from cirrus, it 

 would appear that in a drier atmosphere, when cirrus has 

 ceased to transmit the electric force, cirrocumulus results; 

 while in a moister atmosphere the cirrus gradually subsides 

 into cirrostratus. This origin of cirrostratus may be traced 

 long after the cloud is decidedly formed, by the striated ap- 

 pearance which it presents to the eye when the moon is seen 

 behind it. Mr. Howard remarks, that "when the cirrostratus 

 is prevalent, the lower atmosphere is usually pretty much charged 

 voilh dew or haze, and therefore in a state to conduct an elec- 

 tric charge to the earth." 



From what has preceded, we are enabled to gather, that in 

 the case which Mr. Howard has suggested in pages 149 and 

 150, the general state of the atmosphere was sufficiently moist 

 to favour the production of cirrostratus from the haze resulting 

 from the subsidence of the particles of water in the higher 

 regions of the atmosphere. We may now pass on to the 

 electrical effects consequent on the production of this sheet of 

 haze, or its resulting sheet of cirrostratus. Mr. Howard re- 

 gards the effect as the production of a negative charge in a 

 lower stratum of the atmosphere; he says, "As soon as a 

 sufficiently dense stratum of these particles is formed, we 

 have the superinducing cause at the region tw, m, m, by 

 which the lower air may be rendered negative; and the ac- 

 cumulation of such a haze before rain is not a matter of sup- 

 position only, but of long observation." In immediate con- 

 nexion with this remark of Howard, ir may not be inappro- 

 priate to mention, that during my late discussion of the elec- 

 trical observations at Kew, I found that in most of the in- 

 stances in which negative electricity was observed at Kew, 

 cirrostratus was observed at Greenwich. 



We now turn to the consideration of the production of the 

 cumuloid masses by the condensation in the lower atmosphere 

 of the aqueous vapour emitted by the heated earth. In con- 

 nexion with this, Mr. Howard appears to regard three strata 

 of the atmosphere as contemporaneously existing: — 1st. The 

 region of cirrostratus of course containing much aqueous va- 

 pour in a condensed state, this region possessing (or rather 

 the cloud suspended in it) a positive charge; 2nd, the region 



