ON THE ELECTRIC COLUMN. 2^3 



same space, they ^rst precipif ate \n the vesiculce which form 

 clouds; and \t' the decomposition of the oir continues some 

 time in the same stratum^ these vesiculce collapse into drops, 

 and form rain. 



V. This is one of the causes of the variation of the haro- Variation of 

 meter, not as a prognostic, bnt as a conscfjnence. The abso- thebarometer. 

 lute mass of the atmosphere is constantly changing by these 

 inverse operations. When there is a lon^j duration o^ fine 

 weather over a great extent of country, the absolute quan- 

 tity of azV increases in the atmosphere, by the aqueous va- 

 pour which ascends in it continuing to be transformed into 

 air during the day ; and the barometer ascends, even in parts 

 at some distance where it rains: when on the contrary there 

 prevails over a great extent of country a long continuance 

 of decomposition of air into rain, the mass of the atmosphere 

 decreases, and the barometer falls., even in adjacent coun- 

 tries where there is fine weather. It is not therefore to be 

 expected, that rain and fine weather should be positively 

 connected with certain absolute heights of the barometer; 

 its small motions, when it is more or less high, have the 

 surest correspondence with the local weather; the fall indir- 

 eating the presence of that subtile fiuid, which tends to rfe- 

 cotnpose the air, and the ascent, the cessation of this in- 

 fluence. 



VI. \^, di\\Y\n^ the decomposition of atmospheric air, the Rain alouf. 

 fiuid operating this effect so unites with the ingredients of 

 the electric fiuid, which had entered into the composition 

 of that air, as to form a new compound in which the electric 

 fiuid does not possess its characteristic properties, rain only 

 is produced, with little or no electric symptom ; and this i^ 

 the most common case. But when, from the nature of the 

 new fiuids which come to be spread in that stratum ef the 

 atmosphere, the decomposition of atmospheric air is such 

 as to permit electric fiuid to be produced by the precise in- 

 gredients (i. e. neither more nor less) necessary to its cha-r 

 racteristic properties, it darts suddenly into the air in light-^ Lightning. 

 ning: but this is only a first effect, and not yet thunder, a Thunder, 

 most astonishing phenomenon, consisting undoubtedly in 

 successive detonations, such as the report of caiunons fired in 

 a rapid succession ; and the former deionatiaqs must have 



with 



