Curiosities of Science. 215 



share, which has been taken from the rubber, the latter being conse- 

 quently in a minus or negative state. This theory Professor Faraday 

 considers to be opposed to the distinct characteristic actions of the two 

 forces ; and, in his opinion, it is impossible to deprive any body of elec- 

 tricity, and reduce it to the minus state of Franklin's hypothesis. 

 Taking a Zamboni's pile, he applies its two ends separately to an elec- 

 ti-ometer, to show that each end pi-oduces opposite kinds of electricity, 

 and that the zero, or absence of electrical excitement, only exists in the 

 centre of the pile. To prove how completely the two electricities neu- 

 tralise each other, an excited rod of gutta-percha and the piece of flannel 

 with which it has been rubbed are laid on the top of the electrometer 

 without any sign of electricity whilst they are together ; but when either 

 is removed, the gold leaves diverge with positive and negative electri- 

 city alternately. The Professor dwells strongly on the peculiarity of the 

 dual force of electricity, which, in respect of its duality, is unlike any 

 other force in nature. He then contrasts its phenomena of instanta- 

 neous conduction with those of the somewhat analogous force of heat; 

 and he illustrates by several striking experiments the peculiar property 

 which static electricity possesses of being spread only over the surfaces 

 of bodies. A metal ice-pail is placed on an insulated stand and electri- 

 fied, and a metal ball suspended by a string is introduced, and touches 

 the bottom and sides without having any electricity imparted to it, but 

 on touching the outside it becomes strongly electrical. The experiment 

 is repeated with a wooden tub with the same result ; and Professor Fa- 

 raday mentions the still more remarkable manner in which he has 

 proved the surface distribution of electi'icity by having a small chamber 

 constructed and covered with tinfoil, which can be insulated ; and whilst 

 torrents of electricity are being evolved from the external surface, he 

 enters it with a galvanometer, and cannot perceive the slightest mani- 

 festation of electricity within. 



The Two Threads. A curious experiment is made with two kinds of 

 thread used as the conducting force. From the electric machine on the 

 table a silk thread is first carried to the indicator a yard or two off, and 

 is shown to be a non-conductor when the glass tube is rubbed and ap- 

 plied to the machine (although the silk, when wetted, conducted) ; while 

 a metallic thread of the same thickness, when treated in the same way, 

 conducts the force so much as to vehemently agitate the gold leaves 

 within the indicator. 



Non-conducting Bodies. The action that occurs in bodies which 

 cannot conduct is the most important part of electrical science. The 

 principle is illustrated by the attraction arid repulsion of an electrified 

 ball of gilt paper by a glass tube, between which and the ball a sheet 

 of shellac is suspended. The nearer a ball of another description an 

 tmelectrical insulated body is brought to the Leyden jar when charged, 

 the greater influence it is seen to possess over the gold leaf within the 

 indicator, by induction, not by conduction. The questions, how elec- 

 tricities attract each other, what kind of electricity is drawn from the 

 machine to the hand, how the hand was electric, are thus illustrated. 

 To show the divers operations of this wonderful force, a tub (a bad con- 

 ductor) is placed by the electric machine. When the latter is charged, 

 a ball, having been electrified from it, is held in the tub, and rattles 

 against its sides and bottom. On the application of the ball to the indi- 

 cator, the gold leaf is shown not to move, whereas it is agitated mani- 

 festly when the same process is gone through with the exception that 

 the ball is made to touch the outside only of the tub. Similar experi- 



