386 



•WELLS'S NATURAL PHILOSOPHY. 



Fig. 326. 



Cf 



^ 

 ^ 



Upon working the machine, the outer bells become positively electrified, and 



the middle one, which is insulated from the 

 prime conductor, becomes negative by in- 

 duction. The httle clappers between them 

 are alternately attracted and repelled by the 

 outer and inner bells, producing a constant 

 ringing as long as the machine is in action. 

 It was by attaching a set of beUs of this 

 kind to his lightning-conductor, that Dr. 

 Franklin received notice, by their ringing, 

 of the passage of a thunder- cloud over hia 

 apparatus. 



Let a skein of linen thread be tied in a 

 knot at each end, and let one end of it be attached to some part of the con- 

 ductor of a machine. When the machine is worked the threads will become 

 electrified, and will repel each other, so that the skein will swell out into a 

 form resembling the meridians drawn upon a globe. 



K we ignite the extremity of a stick of sealing-wax, and bring the melted 

 wax near to the prime conductor of a machine, numerous fine filaments of 

 wax will fly to the conductor, and will adhere to it, forming upon it a sort 

 of network like wool. This is a simple case of electrical attraction. The 

 experiment will succeed best if a small piece of wax is attached to the end 

 of a metal rod. 



756. When a current of electricity passes 

 through a good conductor of sufficient size to 

 carry off the whole quantity of electricity 

 easily, the conductor is not apparently affected by its 

 jjassage ; but if the conductor is too small, or too imper- 

 fect to transmit the electric fluid readily, very striking 

 effects are produced — the conductor being not unfre- 

 quently shivered to pieces in an instant. 



The mechanical effects exerted by electricity in passing 

 through imperfect conductors, may be illustrated by many 

 simple experiments. 



If we transmit a strong charge of electricity through water, 

 the liquid will be scattered in every direction. 

 A rod of wood half an inch thick may be split by a strong charge from a 

 Leyden jar, or battery, transmitted in the direction of its fibers. 



If we place a piece of dry writing-paper upon the stand of a universal dis- 

 charger, and then transmit a charge through it, the electricity, if sufficiently 

 strong, will rupture the paper. 



If wo hold the flame of a candle to a metallic point projecting from the 

 prime conductor of an electrical machine in action, tho current of air caused 



"What effect has 

 electricity upon 

 a conductor i 



What experi- 

 ments illustrate 

 the mechanical 

 effects of elec- 

 tricity ? 



