300 



ATMOSPHERIC ELECTRICITY. 



prefenceof the electrometer is not effential in this experiment, 

 we may conclude from it that each conductor placed perpendi- 

 cularly on the earth, has its polarity in the direction in which 

 we have juft explained it. 

 One extremity This (hows why an electrometer indicates a divergence plus 

 ter indtcatesdU'" wnent ' )e P oint ' s touched with the hand in the open air, and is 

 vergence; the foon withdrawn, while there is no divergence when the lower 

 other dues not. part of the wire - u touched> This phenomenon is feen in 

 Weiis's electrometer, even when the wire is not more than 

 three quarters of a foot long. 

 Experiments on From all this it will be feen how deceitful the experiments 

 the aS tlf 0n lhe ele Cliicity of the atmofphere may be; for in the corn- 

 uncertain, mon method, the hand is directed (o be moved from the bottom 

 upwards, towards the point of the electrometer, to deprive it 

 of its accidental electricity, and it is precifely this which com- 

 municates it to it. 

 Theinterven- With refpect to the exceptions which the facts announced 

 rain "fcc.^e- ' aDove nia y be liable to, it mud be obferved that when a ftorm 

 verfes the phe- drives a cloud over the zenith of the obferver, or when rain, 

 hail or fnow falls at the place of obfervation, the phenomena 

 which occur are totally oppofite ; the electrometer gives plus 

 when it is brought towards the earth, and rainus when it is re- 

 but a continued moved from it, &c. &c. But this anomaly is only a tranfient 

 ra ' n ° r a / y effect, and the pretended negative ftate of the atmofphere does 

 by clouds does not exift, either when the rain is of long duration, or when 

 not * the iky is entirely covered with clouds; for in the latter cafe 

 the electrometer is pofitive on being raifed, as when the Iky is 

 clear. The perturbations fpoken of are only momentary and 

 Thefe changes change continually. It is evident that thefe changes cannot be 

 thTatmShL attribll{ecI to the charge of elearicity fet at liberty in the air: 

 of the cloud, it is more probable that thefe maffes of clouds modify the elec- 

 trometer by their atmofpheres, like the tree in the preceding 

 experiment. The perpendicular conductor may be compared 

 to an iron bar, the polarity of which is reverfed accordingly as 

 the fame pole of a magnet is prefented to one or other of its 

 and may be iml- extremities; thefe effects of the meteoric maffes may alfo be 

 titsA ' imitated by conductors ; the fole motion of the hand above the 

 point of an electrometer is fufficient to produce the negative 

 ftate in queftion, and infulation renders thefe effects more 

 fenfible. 



(To be concluded in our next.) 



SCIENTIFIC 



