82 On the Electr'uiti/ of Minerals. 



a stick of wax or gum lac, parliciilarly in the great heala of 

 summer. 



These inconveniences sugQ;ested the idea of employina; in 

 the experiments relative to the ohject in queslion, only 

 bodies susceptible of being electrified by heat, and to make 

 their mutual capacities subservient to the development of 

 their properties. As the two fluids which compose the 

 natural electric fluid of these bodies, before the experiment, 

 remain engaeed in their pores; alter being extricated by the 

 effects of ileal, thev are removed from all external influence, 

 and the electrical stale of the bodies is kept up in the midst 

 of the dampest air. I do not know if there is not even 

 something more striking in those experiments which con- 

 nect the functions of bodies electrical by heat, with those 

 of the magnet, to which thev have so great an analogy, 

 either in consequence of their doul^le polar virtue, or by the 

 law to which the distribution of the two fluids is subjected 

 in their interior. 



I shall now describe the new apparatus which I employ 

 in the experiments in question, and which was made with 

 much care by M. Tavernier, an eminent watch-maker. It 

 is composed of two principal pieces ; the one is a stalk of 

 silver, a b (fie;. 2.) fixed on a round piece of the same metal, 

 and having at its upper extremity a very sharp-pointed steel 

 needle, on^: the other piece consists principally of a rect- 

 angular plate of silver, A A, turned up at both ends, where 

 holes have been made at or. This silver plate is pierced in 

 the middle by a circular hole, in order to receive a small 

 cover of rock crystal which is held by a circle of silver, and 

 by means of two screws, s, z. 



Towards the extremiiies of the inferior surface of the 

 plate Ilk, are fixed two silver wires mi, ny, directed a little 

 obliquely to this surface, and terminatea by two globules 

 /, {) of the same metal. Fig. 3. represents this plate seen 

 from below, and fig. 4. represents the stalk, with the steel 

 needle by which it is terminated. 



When the apparatus is fixed, as we see in fig. 2, the 

 needle in question perforins the ottice of a pivot, which en- 

 ters into a small aperture made in the under surface of the 

 rock crystal cover. The two holes o, r, are destined to re- 

 ceive a tourmaline 1 1' , ov any other bodv of an oblong 

 form, susceptible of being electrized by heat ; and such is 

 the sensibility of the aoparatu.s that a small force which 

 acts bv attraction, or by repulsion, on eittR-r extremity of 

 the body t i' , instantly produces a very perciptible rotatory 

 motion in this body. 



To 



