ELECTRICITY. 



Variation* 



, '* WaS> ' K)WCTer ' Pwpti"''' in town*, in tin- middle of 

 - large squares, on the aides of ijii.-i\ s. but principal- 

 bridges, where he t'oiimi it much ilian in the 



open country. It is more the nlativc th.mlhe absolute 

 height ol' the place of observation thi.t artects the in- 



v of atmo*phcrical electricity. It is stri'ii^. 

 example, at the angle of a terrace rained ulxnil i:> or '.'0 

 feet above the level of tlic country, than in tiie middle 

 of a Hi.t plain, or the top t' a high hill ; tor as the 

 angle ol tiu- terrace is more iiiMil.'tcd, it has with the 

 earth fewer points of contact, which deprive it of its 

 eUvtrieity. 



The intensity of atmospheric electricity is subject to 

 of the cite- great changes in the same place. When the weather is 

 tlie not serene, it is impossible to assign tl;e law of these va- 

 ri.-itioi.-. as it dot s not seem to depend upon the time of 

 the day. or upon any of the known modifications of the 

 atmosphere. '1 >?' tin- i> obvious. \\licn con- 



trary and variable winds prevail at different heights, 

 whcji doudl me rolling above other clouds, those winds 

 and cli.iul.s. which we cannot perceive, influence the stra- 

 tum of air in which the experiment is made, and pro- 

 duce changes, of which we see only the effects. In 

 stormy weather, for i xample, we observe the electricity 

 strong, then become imperceptible ami afterwards re- 

 cover its strength, become positive, and the next moment 

 v e. w it hout any apparent cause for these variations, 

 which .-omctimes occur so rapidly that it is impossible 

 even to note them down. When the weather is rainy, 

 without being stormy, these variations are less sudden. 

 The intensity of the electricity alone varies, being almost 

 always positive in rainy or snowy weather. In cloudy 

 weather, when it is neither rainy nor stormy, the elec- 

 tricity follows nearly the same laws as when the wea- 

 ther is serene. The intensity of the electricity is com- 

 monly diminished by strong winds, which bring the dif- 

 ferent strata of the atmosphere successively towards the 

 ground, and this promotes the uniform distribution of 

 the electric fluid between the air and the earth. 



The state of the air, with the exception of stormy 

 weather, when the electricity of the atmosphere is 

 .strongest, is during the prevalence of fogs, which are 

 always accompanied with a very perceptible electricity, 



Electricity 

 during fog', 



imli-> when they resolve themselves into rain, when 



sometime* no electricity is \ ; 



fog* are pretty cirlain sign of good weather. They ~~ ""V"*' 



i <io not rise to a great height above the Mirf.i. 

 of the i. irth ; and when the low grounds are com, 

 ^ky i> clear on the mountains. In ; 

 L'S conduct to the earth the electricity of the 

 serene air which rcigi's above them. 



In winter and in clear weather, tiaussurr found that Diurnal Ta- 

 the electricity of the air was generally v "nin 



interval which cl'-psid between the time when the fa!- <K ' r . we *- 

 ling of the dew had ceased in the evening, and the in- 

 st int of the rising of the sun. It- intensity then gra- 

 dually increased, and sooner or later, but almost ;,lwa\s 

 before mid-day, it reached a certain maximum, alter 

 which it diminished till the fall of the dew, when it is 

 sometimes stronger than it has been during the whole 

 day. It then gradually decreases (hiring the night, but 

 never becomes imperceptible, it' the weather is peilectly 

 clear. The electricity of the atmosphere has, therefore, 

 n diurnal period like the sea, increa-v.ig and decreasing 

 twice in every iM hours. Its intensity is a maximum 

 some hours alter the rising and setting of the sun ; and it 

 is weakest before the rising nnd setting of that luminary. 



In order to give an example of this diurnal period, 

 M. Saussure has selected the observations of the ' Jd of 

 February 1785, which was one of the coldest <! iv> ever 

 remarked at ( ieneva ; and he has also given the observa- 

 tions made on the day which preceded and followed it. 

 These results arc contained in the following Table. The 

 observations were made 60 feet above the level of the 

 Lake of Geneva. The thermometer and hygrometer 

 were suspended in the open air on a south-west terrace, 

 and the electrometer gave the same electricity as if it 

 had been placed under similar circumstances in an open 

 plain, for the wall of the terrace increased this electrici- 

 ty as much as tlie neighbourhood of the house diminish- 

 ed it. The height oi the barometer is reduced, accord- 

 ing to the method of M. De Luc, to what it would have 

 been if the mercury had been constantly at the tempera- 

 ture of 10 of Reaumur. A weak wind from the south- 

 east prevailed almost constantly on the 21st, -~cl, and 

 23d of February, when the observations were made. 



TABLE, shewing the Electricity of the Atmosphere during three Days, at various Hours of the Day and Night. 



