Hall and Corbino Effects. 315 



of rotation of the secondary coil. F is the fluxmeter reading 

 on reversing the held. 



Thickness of disk. 



F. 



<7R 



0-0505 cm. 

 0-1526 „ 

 0-20315 „ 



165 

 166 

 169 



Mean 



15-3 



14-7 

 15-0 



15-0 



The agreement is very good, especially when it is 

 considered that, in all probability, the disks were cut from 

 different sheets of metal. 



The mutual inductance between the coils and the Corbino 

 disk was also determined by a graphical method. This 

 method, which was purely analytical, gave results in good 

 agreement with those obtained experimentally, as is shown 

 below : — 



M (calculated) 11790 e.m.u. 

 M (experimental) 11860 e.m.u. 



This graphical method was of such a nature that one could 

 investigate the most advantageous form of coil for any given 

 conditions. 



It was tacitly assumed that the flux calculated for a plane 

 passing through the middle of the coil and parallel to the 

 disk is a mean value of the flux in the surface of the coil 

 next to the disk and the flux in the opposite surface. That 

 this assumption is justified may be inferred from the agree- 

 ment of the experimental and calculated values of the 

 inductance. 



A similar assumption was made in the calculation of the 

 inductances for the nickel disks of varying thickness. That 

 this is legitimate is also borne out by the above theoretical 

 determination, since the change in thickness of the disks 

 was only about half of the actual thickness of the inductance- 

 coil used. 



Iron. — This disk was made from a bar of Norway iron, as 

 was the plate used for the determination of the mutual 

 inductance of the two coils and the disk. The inductance 

 was investigated both with and without the external field ; 

 there was no change due to the presence of such a field 

 except for large values beyond 10,000. At this particular 

 point the change was less than 1 per cent. In the study of 



Y2 



