SCIENTIFIC TRACTS. 



NUMBER XXI. 



ELECTRICITY. 



[Continued.] 



IV. EFFECTS PRODUCED BY ELECTRICITY WHEN IN 

 MOTION. 



UNDER this head are to be classed by far the most 

 striking and powerful of the effects of this mysterious 

 agent. When the fluid is in its natural state of diffusion 

 over all bodies, it is, as we have seen, apparently inert 

 and powerless, though we must suppose that it exerts 

 some very important, though secret ajrency in those si- 

 lent processes, by which the course of nature is main- 

 tained. When the fluid is accumulated, so as to exist 

 in bodies in unnatural quantities, or in an unnatural state, 

 while it is kept in this state, it produces only the gentle 

 effects of attraction and repulsion which have been al- 

 ready described. It will be noticed that in all those ex- 

 periments on electrical attraction and repulsion, a motion 

 of the fluid is alluded to, as a consequence of the ar- 

 rangement of the apparatus, yet the attraction and repul- 

 sion are in all those cases, anterior to the motion of the 

 fluid, and consequently are properly to be considered as 

 effects producediby the electricity while at rest. For ex- 

 ample, in the case of the electrical spider, the little ani- 

 mal is attracted by the knob of the jar, while the fluid in 

 the knob is at rest ; it approaches in consequence of 

 the attraction, and, on coming into contact, a portion of 

 the electricity passes from the knob and enters the spi- 

 der. Here is motion, and immediately after it, the bo- 



VOL. i. NO. xxi. 44 



