318 WRITINGS OP JOSEPH HENRY. flSSS- 



same degree for example, we bring in contact with the part 

 to be examined a small metallic ball suspended at the end 

 of a very fine silk thread, (a fibre from a cocoon will serve 

 for this purpose,) and afterwards bring the small ball, which 

 may be called the carrier, in contact with the ball, or as it is 

 called, the knob of the electroscope. The electricity of the 

 carrier will distribute itself, on account of the repulsion of 

 its atoms, throughout the knob, the stem, and the leaves of 

 the electroscope. The leaves being the only movable part 

 will diverge from each other, and will thus exhibit the elec- 

 trical repulsion to the eye. We see from this experiment, 

 as well as from that of the ball touched with the excited 

 glass, that electricity may be transferred from one body to 

 another, and that when it is applied to the end of an elon- 

 gated metallic conductor it instantly diffuses itself over the 

 whole mass. In the experiment we have just described, the 

 body was supposed to have been positively electrified ; but a 

 similar effect would have been produced had it been nega- 

 tively charged. In that case, a portion of the natural elec- 

 tricity of the carrying ball would have been drawn from it 

 by the un-saturated matter of the electrified body, and the 

 ball in turn, when brought in contact with the upper end of 

 the electroscope, would draw from it a portion of its natural 

 electricity — the deficiency extending to the leaves — which 

 would therefore diverge, since according to the theory un- 

 saturated matter repels un-saturated matter. 



If we wish to ascertain whether a body is electrified nega- 

 tively or positively, we transfer a portion of its charge to the 

 electroscope by means of the carrying ball, and then, hav- 

 ing rubbed a rod of glass with a piece of woollen cloth, we 

 bring it near to the electroscope; if the leaves diverge farther 

 when the rod of glass is brought near, the original charge is 

 of positive or plus electricity ; if on the contrary the leaves con- 

 verge, we may consider the electricity as negative or minus; or 

 the same conclusion may be arrived at by rubbing a stick 

 of sealing-wax with the woollen cloth, which becoming nega- 

 tively excited will cause the leaves in the case of a positive 

 charge to converge, and in that of a negative charge to 

 diverge. 



