ELECTRICITY. 501 



1. It is instantaneous. 



It is very common for a lecturer upon electricity, af- 

 ter explaining fully to his class the fact, that when a 

 communication is formed between the inside and out- 

 side of the jar, the fluid passes from one to the other, 

 to request them to form a line by joining hands, 

 and to allow the charge to pass through them all, so as 

 to observe who feels the etfect soonest. But when the 

 line is formed, and one extremity is connected with the 

 outside of the jar, and the individual who stands at the 

 other extremity, touches the knob connected with the 

 inside, the start of the .whole line is precisely simulta- 

 neous. At college this experiment is sometimes tried 

 with some hundreds of students arranged in a long line 

 in the college yard. The one at the extremity most 

 remote from the jar takes hold of a chain which, sup- 

 ported at intervals, returns to the jar, and thus the fluid 

 has to pass through a distance of many hundred feet, 

 but no perceptible difference of time is to be observed. 



Another interesting way of exhibiting the instantane- 

 ousness of the motion is this. A wire connected, at 

 one end with the outside of the jar, is passed around 

 the room, by fastening it against the wall, so that at last 

 the other end returns near to the table. At any remote 

 part there may be a short interruption, across which 

 the electricity will pass by a visible spark, at the pre- 

 cise instant in which the returning end of the wire is 

 connected with the knob of the jar. 



Some English philosophers tried this experiment on 

 a larger scale still. They extended wires, supported by 

 silken strings which they fastened to stakes set in the 

 ground, several miles in length. The discharge was ef- 

 fected through these, and not the slightest difference be- 

 tween the entrance of the fluid at one end of the wire, 

 and its return through the other, could be perceived, 

 though in the interval it must have passed six or eight 

 miles. The motion of electricity may, however, be pro- 

 gressive, it may consume time, and yet not be per- 

 ceptible in so short a distance. Light requires time to 

 pass across any space. This time is very perceptible in 



VOL. i. NO. xxi. 44* 



