ii6 POPULAR LECTURES AND ADDRESSES. 



made to flow through the connecting (J~ tu be 

 will cause it to flow on after it has come to its 

 mean level in the two cisterns, and to rise to a 

 higher level in the one in which it was previously 

 higher, and to sink to a correspondingly lower level 

 in the other. Thus the water-level in each cistern 

 would alternately be above and below the mean 

 free level : the range of motion becoming gradually 

 diminished, in virtue of the viscosity of the water, 

 until after a dozen or two of oscillations, the ampli- 

 tude of each becomes so small that you cannot 

 notice it. Precisely the same thing happens in 

 the case of the discharge of a condenser through 

 a resistance coil of large electro-magnetic inertia : 

 the resistance of the copper wire being like the 

 viscous influence which causes the oscillations of 

 water to subside. If, in his investigations through- 

 out the universe, our traveller could meet with 

 a metal which is about a million times as con- 

 ductive as copper, he would make this experiment 

 with much greater ease ; but it is practicable with 

 copper. It is certain from the observations made 

 by Feddersen, Schiller, and others, that a great 



