ELECTRICAL UNITS OF MEASUREMENT. 1 1 5 



netism (vol. ii. chap. xix.). It is too long to 

 explain the details, but read the mathematical parts 

 of Clerk Maxwell, read the British Association 

 volume of Reports on Electrical Standards, and 

 read Everett's Units and Physical Constants ; get 

 these off by heart from the first word to the 

 last, and you will learn with far less labour 

 than by listening to me. Take a resistance coil 

 of proper form for maximum electro-magnetic 

 inertia, 1 and discharge the condenser through it ; 

 or rather start the condenser to discharge through 

 such a coil, and you will have a set of oscillations, 

 following exactly the same law as the oscillations 

 of the water-level in two cisterns, which, having 

 initially had the free water-level in one higher 

 than in the other, are suddenly connected by a 

 U-tube. Imagine two such cisterns of water, con- 

 nected by a [J~ tu be with a stop-cock, and having 

 the water higher in one cistern than in the other: 

 now suddenly open the stop-cock, and the water- 

 level will begin to fall in one cistern, and rise 

 in the other. The inertia of the water, thus 



1 See Clerk Maxwell's Electricity and Magnetism, sect. 706. 



I 2 



