104 Hare on Electricity. 



strument, lately contrived by me, in which, uninfluenced 

 by the idea, that repulsion is the cause of electrometrical 

 indications, I suspend only a single leaf. A brass ball, one- 

 fourth of an inch in diameter, is so situated, that it may be 

 made to touch the leaf, or retire from it to the distance of 

 and inch, by means of a screw which supports it. (See 

 plate — fig. 1.) This instrument is evidently more simple, 

 and is far more sensitive, than any instrument with two 

 leaves heretofore contrived.* 



It will be admitted, I presume, that the contact between 

 the ball and the leaf must result from attraction, whether 

 the leaf be minus or plus ; and that this would not cease to 

 be true, although a second leaf were, as usual, suspended 

 beside the first. 



In a common electrometer, it is usual to have pieces of 

 tin foil pasted on the glass case opposite the gold leaves. 

 If attraction be exercised between the leaves and coatings, 

 when moveable, it must also be exercised by the fixed coat- 

 ings thus pasted on the glass. It is therefore established, 

 that when coatings, whether moveable or fixed, are em- 

 ployed, the divergence is not caused by repulsion. It can- 

 not, then, be reasonable to ascribe it to repulsion, though 

 no coatings should be present, as when the leaves are sus- 

 pended where nothing can attract them unless the sur- 

 rounding air; especially as the air may be shown competent 

 to perform the same office as the coatings, though not so 

 well, on account of its presenting less matter within the 

 same space. The lightness and mobility of the air, is no 

 obstacle to this conclusion. When equally acted upon in all 

 directions, as it must be in the case in point, air resists like 

 an arch, or an elastic solid. The electric attraction may 

 have a tendency to condense it about the sphere of excite- 

 ment, butcannot move one portion more than another. This 

 -Opinion of the agency of the air, is supported by the fact, 

 tha,t, in proportion as an exhausted receiver is larger, so will 

 the difficulty of producing a divergency in the electrometri- 

 cal leaves, situated within it, be increased. It would be 

 difficult to procure a receiver so large, that gold leaves 

 might not be made to diverge electrically in it, when ex- 

 hausted ; but leaves of light paper, which will easily be 



* By means of an instrument with a single leaf, since constructed, I am 

 enabled to detect the electricity produced, by one contact, between 'a 

 cppper and zinc disk, each six inches in diameter. 



