Peirce — Magnetic Properties at High Excitations. 5 



K and L due to a reversal of the current in the exciting circuit 

 of the yoke, corresponding values of ZTand B. 



The ballistic galvanometer used in this work had a period 

 so long that no appreciable error was caused by the fact that 

 several seconds were necessary to bring about a complete 

 reversal of magnetization in the magnetic circuit. The gal- 

 vanometer has been described under the letter V, in the Pro- 

 ceedings of the American Academy of Sciences in December 

 of last year. 



The test coils were wound by Mr. Coulson, who has helped 

 in all the work. 



The iron of which the magnet core described above was 

 made is here denoted by the letter P, while Q denotes a similar 

 very pure specimen of Norway iron obtained from a new 

 source. 



Table I. — Specimen of Norway Iron (P) Magnetized in Massive 



Yoke. 



(Free length about 80 millimeters, diameter 12'67 millimeters.) 



/ 

 1513 

 1566 

 1650 

 1692 

 1705 

 1713 

 1720 

 1723 

 1729 

 1730 

 1731 

 1732 

 1733 

 1733 



The maximum value of 1 seems to be in the vicinity of 

 1733, and for large values of the excitation corresponding 

 values of H and B may be computed by means of the equa- 

 tion B=H+21780. 



This record shows conclusively that the magnetic perme- 

 ability of this iron under strong excitation is extraordinarily 

 high and that the failure of the magnet mentioned at the 

 beginning of this report was not due to poor material in the 

 core. The real source of the difficulty is disclosed by an 

 examination of the diagram shown in figure 4. This was 

 obtained by sprinkling iron filings upon a horizontal piece of 

 cardboard which rested on the toroid as it lay upon the floor 



H 



B 



150 



19160 



200 



19920 



300 



21040 



400 



21660 



500 



21920 



600 



22130 



.700 



22300 



800 



22450 



1000 



22720 



1200 



22940 



1400 



23180 



1600 



23380 



2000 



23780 



2500 



24280 



