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XLII. On a new Electroscope. By M. Melloni*. 



WHEN a conductor in a natural state is brought near an 

 electrified conductor, it renders imperceptible a portion 

 of this electrical state, and by communicating its positive tension 

 to the masked fluid in proportion as the perceptible fluid quits 

 it by dispersion, prolongs the duration of the electric charge. 

 On the other hand, it is well known that this effect is derived 

 from the opposite electricity, developed by induction, in the 

 nearest part of the induced body, and that the electricity, homo- 

 logous with that of the inductive body, appears in the most 

 distant portions, where it is distributed in proportions increasing 

 with the diminution of the radius of curvature. 



A combination of these three data, led me to conceive the 

 possibility of constructing an electroscope of extreme sensibility, 

 and capable of remaining electrified in either direction for a 

 much longer time than any known apparatus of this description. 

 The result has completely answered my expectations, and as I 

 am convinced that this new instrument will become exceedingly 

 useful in electrical researches of several kinds, I shall endeavour 

 to describe it with all necessary details. 



A is a little metallic cup, furnished with two long wire 

 appendages, D, which are soldered to opposite points of its upper 

 margin ; it communicates, by a conductor passing through a 



* From the Comptes Rendv.% Dec. 11, 1854, p. 1113. 



