ELECTRICAL UNITS OF MEASUREMENT. 1 17 



lumber of oscillations can be observed, and that 

 le period, or semi-period of oscillation, can be 

 itermined with considerable accuracy. 

 If our scientific traveller wishes, by this beautiful 

 experiment, to determine once for all his time 

 reckoning, let him proceed thus. Let him take 

 a coil, of which he knows the dimensions perfectly, 

 having already gone through the preliminary pro- 

 cess of measuring its electrical dimensions ; or if 

 he cannot measure these with sufficient accuracy 

 (and there is enormous difficulty in finding the 

 electric dimensional qualities of a coil by measure- 

 ment), let him do it partly by direct measurement of 

 its length and of the linear dimensions of the figure 

 into which it is wound, and partly by comparing 

 it electro-magnetically with other coils. By an 

 elaborate investigation he can find the electro- 

 magnetic inertia of the coil in terms of his 

 centimetre. And here, again, there is a curious 

 kind of puzzle and apparent incongruity, when I 

 say that the electro-magnetic inertia equivalent 

 of a coil is a length, and is measured as a numeric 

 of centimetres. Let him make a condenser, and 



