PEIRCE. 



MAGNETIZATION IN IRON. 



131 



No. 72) so that it became automatically charged at the terminals of R 

 just as the main switch was reversed, and the charge could then be 

 measured at our ease four or five seconds after the switch had been 

 thrown over. By these means we avoided the delay which would 

 have resulted if we had been obliged to read the amperemeters before 

 the reversal. 



Besides this slowly moving 

 ballistic galvanometer, we 

 used three other mirror gal- 

 vanometers, one for the 

 condenser throws, one for 

 the potentiometer, and one 

 for the accurate comparison of 

 our inductances, and in addi- 

 tion, a large standard labo- 

 ratory amperemeter (W), by 

 Weston, which could l^e 

 checked at any instant 

 against the potentiometer. 

 This beautiful instrument 

 has an engine divided scale 

 31 cms. long. 



At very high excitations, 

 the reversal of any switch of 

 ordinary construction gives 

 rise to a very unpleasant ex- 

 plosion, and we often made 

 use of a large controller (/v) 

 constructed by the General 

 Electric Company for use 

 upon electric cars. This was 

 very kindly lent to us by 



Mr. F. W. Lieberknecht, and Figure 6. 



served an excellent purpose. 



We do not need to describe a large number of auxiliary amperemeters 

 and galvanometers used in our work. 



The Use of Condensers in the Inductive Secondary Circuit. 



The inductance in the secondary circuit, which contained the test 

 coil or coils, the secondary coils of the inductance standards, and the 



