JJ ATMOSPHERIC ELECTRICITY, 



cIe<5trometer, by this fame action, which depends on the divifioif 



of the eledtricity, and this explains the fudden changes wliicl> 



Tupervene in the pofiMve or negative eledric flale of the earth ; 



it is not even probable that the clouds podefs in themfelves a 



negative eledricity, or that the vapours of water fliould be 



Thcpofitivc or always in this (late. Mr. Erman thinks he can prove that the 



"^utoos^va^oar '^P""*^^ ^^ water are only negative when the body from which 



depends on in« they proceed is inCuiated; but that they become pofitive as foon 



ruiation. ^^ [^ [^ brought into contad with the earth. Rain, after its fall, 



leaves bodies in the ftate of ?)iinus electricity^ which is agreeable 



to the preceding experiments ; fnow produces this efFe6l fa 



much the better, as it leaves the furrounding air in a ftale o£ 



drynefs, which augments its infulating properties. 



Influence of the The clouds which have a tendency to rain or fnow muft ne- 



doiids on the ceffarily produce their influence on the ground, and it is for thij> 



reafon that the oppofttion of the cloud and the ground is fo 



quickly manifcfted. It would be interetiing to explain the 



complication arihng from the variations which the electricity 



of the earth undergoes, as well with Fefpeft to its fpecies 



as to its intensity, and Mr, Erman is at prefent engaged in this 



fubjecl. 



The different With rcfpe6l to the variable degree of the pofitive divergence 



phenomena of ^f ^j^ infuhvted point fixed in the earth, it may perhaps be at- 



the divergence ., i i • /- , r 



of an infuiated tnbuted to the greater or lefs conduCtmg quality of the fur- 

 point explained rounding air: the point, when it is very well infuiated from 

 *lhe earth, ftiows a certain degree of pofitive charge when the 

 air is infuiated fo that eleClricity cannot be communicated to 

 it ; it fliows zero when the conducing power of the air is near- 

 ly equal to the rapidity with which the charge is made j and 

 negative when this power is very firong. Thefe phenomena 

 are thus explained by the fame law. 

 Probability that Mr. Erman has alfo fuppofed in his memoir that there is not 

 there IS no free ^y^y quantity of elcdricily difengaged in the atmofphere ; but 

 aimofphere. he does not however aflert that this is firiCtly the cafe : he has 

 only fought to. draw the attention of philolbphers to this fubjed, 

 and to fliow that thcfe phenomena are equally well explained 

 by the fpKere af aftivity of the eleftricity. 

 Cottvemence of The experiments are very eafily made, and the eleClroraeters 

 th£ inftrumcnts. he ufes are very portable ; for when the leaves of gold are 

 placed on one fide of the cylinder, motion cannot occafion 

 any accident. With refpeft to the flicks, they may be made o^ 



feveral 



