ON THE ELECTRIC COLUMN. g.^ 



diflferent, quantities of ^wapora/erf teaser in the same space; 

 and combining them, we have formed tables expressing the 

 different effects of heat on moisture, correspondent to diflle- 

 rent quantities of evaporated water in the same space, and 

 to the changes of heat in each of these quantities ; from 

 which tables, after having observed the hygrometer and the 

 thermometer in any part of the atmosphere, the quantity of 

 evaporated water contained in one cubic foot of that air is 

 determined. These entirely distinct experiments have proved 

 the constancy of the laws prevailing in these effects, by the 

 astonishing agreement of our tables, though determined by 

 very different instruments and processes : an agreement 

 which I have shown in the already mentioned papers to the 

 Royal Society. 



Art. VII. This determination of the effect produced on 

 moisture^ i. e. on the indications of the hygrometer, by the 

 changes of heat, in a mass of air wherein the quantity of 

 evaporated water remained the same, was most essential in 

 meteorology; and in particular it was indispensable for the 

 decision of the question, whether the production of dew 

 were principally owing to the cooling of the atmosphere; 

 which ap]>eared the most natural explanation, but on which 

 however there were sufficient reasons of doubt to produce 

 the obscurity which remained on this phenomenon; because 

 nothing could be either determined or proved, concerning 

 the real effect pf the diujinution oi heat on evaporated water, 

 without such experiments as above defired ; and 1 couie 

 i]pw to their immediate application to the phenomenon of 

 dew; in consequence of some observutions which were also 

 separately made by Mr. de Saussure and myself. Towards 

 sunset and in the beginnirig of the night, moisture increases Aqueous ra- 

 in the air much more rapidly ; and after sunrise and in the l'^"'' '"/*><^ »•' 



' •'. dinnn >lies in 



first part of the day, f/r^«es5 increases also much more ra- tlie mori.mt; 

 pidly — in both cases, comparatively with the corresnondent |*'^d '"c»e;i>es 



1 r I 1 1117 Til' 111 the evening, 



changes of neat—, than would be the case, did the same 



quantity of evaporated water remain in ihe air. This is a 

 very succinct account of our experiments and observations 

 concerning this object, the particulars of which may be seen 

 in our respective works i but it is sufficiently distinct to al- 

 low rae here to conclude, that thus has been pointed out 



one 



