258 *IN THE ELECTRIC COLUMN.^ 



one of the greatest questions and objects of inv€Siigatloi>, 

 concerning terrestrial physics, namely : what is the cause of 

 the disappearance in the atmosphere of the greatfest pert of 

 the aqueous vapour which it before contained, when the sun 

 ascends on the horizon ; and of the increase of its Quantity, 

 when the sun is setting; while the very reverse shouW have 

 been expected from all the hitherto known causes ? (as I 

 shall show hereafter). To this investigation 1 shall now pro- 

 ceed as far as known phenomena will lead me. 

 Changesjnthe Art. VIII. I shall first mention a' very important course 

 Iht^atmo'^ '^^^^^ observations of Mr. de Saussure concerning the change* 

 sphere <=b. hi the electric sta^e oi' the atmosphere. He had erected a 

 de Saussure"^ High conductor, in a favourable situation, on the brow of a 

 hill in Geneva. The lower part of this conductor was con- 

 nected with an insulated pair of pith balls, the divergences 

 of which indicated thf" differences between the electric state 

 of the upper air, and that in which the balls stood : he ob-' 

 served during many years the diurnal variations of this cfi^ 

 Jerence; and the main result of these observations is the 

 following. In common weather, i. e. when no particular 

 cause disturbs the course of the usual operations going on 

 in the atmosphere during each period of 24 hours, the quan- 

 tity of electric Jiuid increases in it from sunrise till some 

 time in the afternoon ; as is seen by the increase of a pori- 

 five divergence of the bolls. The new electric Jluid, the for- 

 mation of which is thus indicated, accumulates in the air, 

 because it is transmitted but slowly to its lower part near 

 the ground. But afterward, when the hygrometer shows a 

 beginning of increase of moisture in the atmosphere, th© 

 divergence of the halls begins to decrease ; and when at last 

 tZ<?i(j is forming; \\iQ electric equilibrium is soon established 

 between its upper and lower parts, the whole of the electric 

 The diminu- Jiuid formed in the day passing then into the ground. Now, 



tion of electric -^ -g (juring the first of these periods, that d7u»<?5tf increases 



fluid in ihe at- ^ -^ i i 



nio-phere con- in the atmosphere much more than would happen by the 



nected with game increase of heal, did only the same quantity of aqueotis 

 aqueous va- vapour subsist in it as before sunrise ; while on the contrary 

 F""""' its quantity ought to increase by a greater evaporation being 



produced on the ground, which dries when heated by the 

 sun. Hence it appears, that there is some connexion be- 

 tween 



