254 Mr. W. S. Jevons on the Forms of Clouds. 



It is so perfectly insulated by the non-conducting property of 

 gases, that only a single particle can be discharged at once. Now 

 when this air rises into the body of a cumulose cloud, the preci- 

 pitated watery particles being good conductors, will rapidly col- 

 lect upon their surfaces all the electricity of the air in which 

 they are immersed. 



34. But it is characteristic of a rain- or storm-cloud that the 

 watery particles become separated from the air ; they sink, sub- 

 side and coalesce, while the air, freed from their weight, rises into 

 higher strata. Surely this air will also be deprived of its whole 

 electric chai'ge, which will collect upon the cloud as the electric 

 fluid of the glass plate upon the metallic conductor. Now as 

 the particles of the cloud gradually coalesce into large sphe- 

 rical drops, the total superficial conducting surface is vastly 

 diminished, and the tension of the electricity is raised to such a 

 pitch, that it must finally overcome the resistance of the non- 

 conducting atmosphere and discharge itself with the earth which 

 is in the opposite electric condition. And so long as a current 

 of moist electrified air enters the cloud from beneath and passes 

 out at the summit deprived of moisture and electricity, must the 

 continually renewed tension of the electricity be relieved by 

 repeated flashes of lightning. 



35. It does not escape me that many apparent objections may 

 at once be urged against this theory ; for instance, the fact that 

 rain is not always accompanied by lightning, and that in a 

 thunder- storm capricious changes in the kind or sign of electri- 

 city often occur. With regard to these I will only remark, that 

 though this theory does not include them, it does not, as far as 

 I can see, exclude them : there is nothing apparently irrecou- 

 cileable in them. I have attempted to show how the cumulose 

 precipitation of rain may be accompanied by the concentration 

 of electric force, but into the modifying conditions of the latter 

 I do not now enter. 



36. I conclude by subjoining, in as bi'ief terms as possible, a 

 statement of the conclusions arrived at in this paper, or the pre- 

 vious one of July 1857. 



1. The cirrus is produced by the interfiltration of two moist 

 bodies of air, of which the lowest possesses the highest tempera- 

 ture and the least specific gravity. 



2. In the acknowledged mode of production of the cumulus 

 by an ascending current of warm moist air, it has been usual to 

 overlook some cause which operates to check the upward motion 

 soon after precipitation has commenced ; of this effect the weight 

 of the precipitated watery particles forms at least partially the 

 cause. 



3. When partial subsidence or separation of the watery cloud- 



