598 WINTER'S ELECTRICAL MACHINE. 



plane happens to be considerably greater than the positive of the 

 electroscope, in which case the latter is neutralised by a portion of 

 the former, and the remainder of the negative charge of the proof- 

 plane, diffusing itself over the electroscope, causes a greater diver- 

 gence of the leaves than the positive charge did before. 



/If the rubber is connected with the ground by a 

 conducting wire or small metal chain, vivid sparks may 



be drawn from the conductor if another conducting 

 body is brought near it. A machine of the size re- 

 presented in fig. 315 will give sparks 10 cm long from 

 the small brass ball, and of about half that length from 

 the conductor. That the sparks are longer when drawn 



.from the smaller ball, follows from what has been 

 proved previously, viz., that electrical tension is greater 

 at a narrow projecting part of a conductor than at a 

 part which has a comparatively flatter surface. 



Similarly sparks of negative electricity may be drawn 

 from the rubber, if the conductor is placed in conduct- 

 ing connection with the ground while the rubber is 

 insulated. These sparks, however, are smaller. The 

 reason is, that although exactly as much positive elec- 

 tricity is developed on the conductor as negative on 

 the rubber, more negative electricity is dissipated in 

 consequence of the rubber being much nearer to the 

 wooden support of the machine. 



To obtain large sparks the flat palm of the hand should be 

 brought near the -conductor ; not the hairy exterior, because the hairs 

 act like points and, therefore, diminish the electricity of the con- 

 ductor. Still better is a rather large round body of metal, for 

 example the convex side of a smooth tablespoon, which is held in 

 the hand and brought near the conductor. 



The best way of connecting either the rubbers or the conductor 

 with the ground is to use spirals of thin wire, closely wound. 

 They are provided with hooks made of somewhat stouter wire, and 

 soldered to the ends. 



