-1859] WRITINGS OF JOSEPH HENRY. 320 



thus insulated. is a long cylindrical metallic conduc- 

 tor, supported by a rod of shellac or sealing-wax d, on stand 

 e, having a glass stem. 



Now each of these metallic bodies contains its natural 

 share of electricity, and as long as this continues to be the 

 same no electrical effects are exhibited; for although the 

 natural electricity of A will repel the electricity of 0, yet the 

 matter of A will attract it with an equal force, and hence 

 there will be no perceptible effect. Let us however suppose 

 that there be imparted to the globe A a redundant quantity 

 of electricity, then the equilibrium in the conductor will 

 be disturbed; the repulsion of the redundant fluid will be 

 greater than the attraction of the un-saturated matter, and 

 hence a portion of the natural electricity of will be driven 

 down to its lower end, and consequently the upper end will 

 become negatively, while the lower is positively electrified. 

 It must be evident therefore that between the two extremes 

 there w^U be a point near the middle which will be in its 

 ordinary condition. 



These inferences may readily be shown to be true by 

 observing three movable pith balls suspended by linen 

 threads, one near the top, another at the middle, and the 

 third at the lower end. Those at the extremities will 

 diverge, exhibiting excitement, while the one at the mid- 

 dle will remain unmoved, indicating that this point is 

 in a natural condition. To be assured that the upper end 

 is negatively electrified, and the lower positively, it is only 

 necessary to rub a stick of sealing-wax with woollen cloth, 

 and bring it in succession near the two balls ; the upper 

 one will be repelled and the lower one attracted ; or we may 

 arrive at the same results by touching in succession the two 

 extremities and the middle of the conductor with the small 

 carrier ball a, and applying it to the knob of the electro- 

 scope B. 



If the conductor be removed laterally to a distance from 

 under the charged globe, the excitement will disappear, the 

 atoms of natural electricity, by their mutual repulsion at 

 the lower end, and attraction for un-saturated matter at 



