'100 On the Frankliman Theory 



passage the last-mentioned bodies afford to this fluid ; in 

 the first case, it finds an easy passaoe to any conducting 

 Substance presented at a convenient distance, and becomes 

 immLdiately discharged ; but in the latter case, it acquires 

 ?.ny electricity with considerable difficulty, and, in order to 

 induce it, must be touched several times and in different 

 parts by an electrified body. A curious expernnent ot" pro- 

 fessor Lichtenbcrg, of Gottingen, deserves to be cited 

 upon this occasion (Cavallo, 72) : he first excised an elec- 

 tric plate, upon which he placed some metallic body of a 

 convenient shape, and to this he communicated an electri- 

 city contrary to the one e^xcitcd : then removing the metallic 

 body by means of an electric, he shook some finely pow- 

 dered resin over the electric plate, which fell over those 

 parts onlvvvhich had been in contact v/ith the metallic body, 

 iorming radiated appearances. This description accords witli 

 a plate excited negatively, and a body positively electrified : 

 but if the electricities are chan£;;cd, the circumstances will 

 be reversed also, and the powdered resin instead of seeking 

 those parts touched by the metallic body will obviously 

 avoid them. — At first sight, no reason appeared for this 

 variation, since both electricities attract an unclectrified 

 body ; but, upon more accurate examination, Mr. Cavallo 

 found that the mere action of falling produced a degree of 

 excitation in the powdered resin, which of course became 

 negatively electrified, and could in that state be attracted 

 only by the contrary electricity. Thus, in the first instance, 

 where the plate was negatively electrified and the parts in 

 contact with the metal positive, the powder also in a nega- 

 tive state attached itself to the positive : — in the latter in- 

 stance, the plate being positive, and the parts in contact 

 negative, the powder also negative would attach itself to 

 the plate, and avoid those parts endued with an electricity 

 similar to its own. 



Thus far the path wc have trodden does not seem encum- 

 bered with any serious diPnculties, but the observed phae- 

 nomena require an addition to this hypothesis v»'hieh is not 

 very easily explicable : in charging a Lcyden phial it is ob- 

 vious, from various experiments, that while one side is re- 

 ceiving the other is emitting. Let a phial be insulated, 

 and the knob of a second phial placed at a short distance 

 from its external coating; every spark from the prime con- 

 ductor to the knob of the first phial will be followed regu- 

 larly by another spark fron> its outside coating to the knob 

 of the second pliial, having to the senses all the appearance 

 .of ^ free passage through the glass ; but if there were a 



fiX<? 



