252 Electricity and Galvanism. 



although you may have taken the precaution to connect the rubber 

 with the table or floor by means of a metallic conductor, still that 

 little or no electricity is obtained on revolving the glass. This will 

 generally be found to depend upon the badly conducting table, or 

 floor, by which a sufficiently ready means is not afforded for the 

 complete restoration of the electric equilibrium of the rubber, when 

 destroyed by the friction of the revolving cylinder or plate against its 

 surface. This difficulty is best overcome, in London and large towns, 

 by connecting the rubber, by means of a long copper wire, with a branch 

 of the leaden pipes through which the house is supplied with water. 

 By this plan a ready communication is afforded by a good conductor 

 with the great reservoir of electricity — the earth. 



Having thus got the machine in good action, on revolving the 

 cylinder or plate, and presenting the hand or a piece of metal towards 

 the prime conductor, a series of vivid sparks, attended with a loud 

 snapping noise, will pass between them. In this arena, I felt that 

 any remark connected with the theory of the excitation of elec- 

 tricity by the machine would be quite misplaced, as I feel that all I 

 have the honour of addressing must be most fully acquainted with 

 every thing pertaining to this branch of physics. There is, however, 

 a popular error so generally believed, that I must venture to allude 

 to it ; the error consists in regarding the electricity of the prime con- 

 ductor as derived from the revolving glass, the latter being regarded 

 as pumping electricity from the rubber, and thence from the earth. 

 Now the fact is, that not an atom of positive electric matter leaves 

 the glass to pass to the conductor. The cylinder or plate, rendered 

 positive by friction against the rubber, merely acts upon the electri- 

 city naturally present in the prime conductor by induction decompo- 

 sing it into the component elements, attracting the negative fluid, 

 which, accumulating pi a state of high tension, or elasticity, dart off 

 towards the cylinder to combine with the positive fluid free on its 

 surface, reconstituting the neutral compound : the prime conductor 

 is thus left powerfully positive, not by acquiring electricity from 

 the cylinder, but by the abstraction of its own negative element. 

 Again, the sparks which appear on approaching the hand to the 

 conductor are often called 'positive sparks, when, in truth, they are 

 nothing of the kind, being, indeed, a series of luminous discharges 



