i.i \\VIII. ATMOSI'IIKKir I'll.KCTKK'ITY. 201 



rota I ion, sliikni". against a eaid. or from the Moles of U NM'CM 

 attached to the ;i\is. I'. \\ ;is thus lli:il I 'i oles.,i >i \\ 'In '.\ Islone 

 loin id (lie mil 1,1 r \\ Inch he employed in his ex pel imenls made 

 SOD i , ' vol ii I it HIM ill u Hecoiid ; and, as (he an 'idai volootty Of llu- 

 rellecled ima'c in a re\ ol\ in; 1 ; mirror is double lhal of llic minor 

 i I sell', mi aieMilar deviation ol % olio de;',iee in llic appe. nance ol 

 llic l\\o spark:, would indicate an interval of the ;> i li,(HHM li of a 

 .second ; the de\ lalion of hall a de-ire \\.mld, Iheiel'nrc, indicale 

 inoie than llu^ mil liolll h of a, second. The n e ol -.oiind as a 

 inea me ..I' velocity is a happy illlist fill ion of the connexion of 



Ill possesses a powerful electrical tension, and the atmos- 

 phere w hen drai is almost always positively dechie. lr. dec 

 hi, n\ is slroni-er in winter than in summer, dnrni", the day 

 than in the nidil. The intensity increases for two or llnee 

 horns fioin the lime of sunrise, eonios lo a maximum lie! ween 

 seven and eidil, then decieases towards ihe middle of I he day, 

 .u M\ es al its minimum helween one and I w o, and a-am an-nieiil s 

 as the sun declines till ahou! Ihe I inn- ol sun.,-1 , afler w hidi u 

 diminishes and conlmnes leehle dnini", the mdil. The mere 

 colldeilsalion of v a pom is a soin ce o| a I mosphei ie dee I M, 1 1 \ ; hnl 

 allhondi it is alsopiodneed l-v the vapour that rise* from the 

 surface of I ho earth, it. is not under all circumstances. INI . I 'ondlet 



found that elccliicilv is oldv developed w hei i arconi pa 1 1 led hy 

 chemical action : I oi example, w hen the water w hence the \ a pour 

 proceeds contains lime, chalk, or any solid alkali, negative doc., 

 trieilv, i . pi od n, ed ; and when it holds in solution eilhei -a ,, acid, 



of I he sails, I lie v a poll I is psi 1 1 \ d \ dee trio. Besides, I he 

 ofeailh with sail and fresh water i',cnerales posil ivo dee 

 and the coiilacl of liesh and salt currents of \valer 

 ', so lhal the ocean must alloid .1 -i,.il Sllpplv lo I he 

 ier< 1 ; hence I hundeislorms are most fre t |uenl near the 

 hill as declncilv ol one kind or another is developed 

 whenever the molecules of mailer aiedeian ,d lim then naliir.il 

 stale of e(|uilihrium, iheie mn si he ma n \ par I lal variations in t ho 

 electric si ale ol I ho air. \\'hen the inv isihh- \ a pom rises charged 

 with t'loctrieiiv into the I'old icMons of the atmosphere, ii is 

 condensed mlo ('loud, m which the tension is increased heeauso 

 (lie electricity is con lined to u smaller space ; and if I he eon den- 



