CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



ON THE ELECTROMAGNETIC AND THE THERMO- 



MAGNETIC TRANSVERSE AND LONGITUDINAL 



EFFECTS IN SOFT IRON. 



By Edwin H. Hall and L. L. Campbell. 



Presented February 8, 1911. Received Februarys, 1911. 



For many years past the electrical and thermal properties of a cer- 

 tain kind of wrought iron have been, from time to time, under investi- 

 gation in this laboratory, and a number of papers ^ giving the methods 

 and results of this study have already been published. The present 

 paper has to do with the so-called Hall effect and the allied effects in 

 the same kind of iron. These are so numerous and so unfamiliar to 

 ordinary observation that it seems well to give an enumeration and 

 brief description of them, somewhat like that given by H. Zahn ^ in 

 his comprehensive paper on such phenomena. 



In each of Figures 1-4 the rectangle, with very short side projec- 

 tions, or arms, represents pretty accurately, halfscale, the broadside of 

 one of our " plates " of iron, which were each about 5 cm. long be- 

 tween heavy terminal blocks of copper (see Figure 7), and about 2 cm. 

 wide. The circle indicates the size of the flat face of each pole of the 

 electromagnet, the arrow showing the direction of the magnetizing 

 current. 



Description of the Transverse Effects. 



Hall Effect. — Figure 1, in which EE is the longitudinal electrical 

 current, and E'E' is the transverse electrical current due to the action 

 of the magnet, shows the Hall effect, positive, according to the ordi- 

 nary convention as to the sign, in this case, the equipotential line which 

 would naturally extend straight across between the arms being rotated 



1 These Proceedings, 41, May, 1905; 42, March, 1907. 



2 tjber galvanometrische und thermomagnetische Eflfekte, Jahr. d. Rad. u. 

 Elek., 5, 166-218 (1908). 



VOL. XLVI. — 40 



