388 



WELLS'S NATURAL PHILOSOPHY. 



one conducting substance to another, ia generally attended 

 with an exhibition of liglit. 



Tho strongest electric charges that can be accumulated 





Must light be 



regarded as a in a body Will never afford the least appearance of light so 



P'"°'J^['7 *"' long as a state of electric equilibrium exists, and the electric 



fluids are at rest. Light, therefore, must not be regarded as 



a property of electricity, but as tho result of a disturbance occasioned by 



electricity. 



,.,^ , ^, The fur of a cat sparkles when rubbed with the hand in 



Wnv Q068 tno 



fur of a cat cold weather. The reason of this is, that the friction between 



oparklo ? ^Y\Q hand and the far produces an excitation of negative elec- 



tricity in the hand, and positive in the fur, and an interchange of the two 

 is accompanied with a spark, or appearance of light. 

 What i« the When the finger, ^^^^ 32, 



form of the or a bras3 ball at 

 fcliictric spark ? ^j^^ ^^^j ^f ^ ^od, is 



presented to the prime conductor 



of an electrical macliine in action, 



a spark is produced by the passage 



of tho fluid from tho conductor to 



the finger or tho metal. This 



spark has an irregular zigzag form, resembling, more or less, the appearance 



of lightning, as shown in Fig. 327. 



Upon what does The Iciigth of the electric spark will vary 

 eiectHc'"* spark "^i^h the powcr of the machine. A very 

 depeud? powerful machine will so charge its prime 



conductor, that sparks may be taken from it at the 

 distance of 30 inches. 



Ifthepartofei- FiG. 328. 



How doos a, 

 point influence ther of the clectri- 



^Ih^^^r cally excited bod- 

 ies which is pre- 

 sented to the other has tho form 

 of a point, the electric fluid will 

 escape, not in the form of a spark, 

 but as a brush, or pencil of liglit, 

 the diverging rays of which have sometimes a length of two or three inches. 

 Fig. 328 represents this appearance. 



A substance parting with electricity generally exhibits an irregular spark, 

 or flash of light; while a substance absorbing electricity exhibits a brush or 

 glow of light. 



MTiat is the The rapidity of the electric light is marvel- 

 Sric"BpLkf ous : and it has been experimentally shown 



