ELECTRICITY. 85 



two bodies exhibiting states of electricity of the contrary 

 denominations. Until this subject was investigated by Fara- 

 day, the intervening non-conducting body or dielectric was 

 supposed to be purely negative, and the effect was attributed 

 to the repulsion at a distance of the electrical fluid. Fara- 

 day showed that these effects differed greatly according to the 

 dielectric that was interposed. Thus they were more exalted 

 with sulphur than with shellac ; more with shellac than with 

 glass, &c. Matteucci, though differing from Faraday as to 

 the explanation he gave, added some experiments which prove 

 that the intervening dielectric is molecularly polarised. Thus 

 a number of thin plates of mica are superposed like a pack 

 of cards ; metallic plates are applied to the outer facings, and 

 one of them electrified, so that the apparatus is charged like 

 a Leyden phial. Upon separating the plates with insulating 

 handles, each plate is separately electrified, one side of it 

 being positive and the other negative, showing very neatly 

 and decisively a polarisation throughout the intervening sub- 

 stances by the effect of induction. 



Indeed, chemical action or electrolysis may, as I have 

 shown, be transmitted by induction across a dielectric sub- 

 stance, such as glass, but apparently only while the glass is 

 being charged with electricity. A wire passing through and 

 hermetically sealed into a glass tube, a short portion only pro- 

 jecting, is made to dip into water contained in a Florence 

 flask ; the flask is immersed in water to an equal depth with 

 that within it ; the wire and another similar wire dipping 

 into the outer water are made to communicate metallically 

 with the powerful electrical machine known as Rhumkorfs 

 coil ; bubbles of gas instantly ascend from the exposed por- 

 tions of the wires, but cease after a certain time, and are 

 renewed when, after an interval of separation, the coil is 

 again connected with the wires. 



The following interesting experiment by Mr. Karsten 

 goes a step farther in corroboration of the molecular changes 



