694: 



Prof. E. P. Adams and Mr. A. K. Chapman 



of wire by the circular current in the metallic disk when the 

 radial current is reversed in direction. The disk and its 

 mounting with the coils is shown in the accompanying 

 diagram. A. represents the disk, soldered to a brass ring, D, 



D 



H >M 



Sggg^, 



*E^ 



^»i\m\\\\\\\\\\\\\^^ G 



tvummuuuumu um 



which screws to the brass plate E. A short copper rod, B, 

 is soldered to the disk, and into this the copper wire G screws. 

 The plate E has eight very fine radial saw-cuts which pre- 

 vent circular currents flowing in it. Failure to take this 

 precaution seems to be the cause of Corbino's not obtaining 

 his effect in copper. To this plate a copper tube F is soldered. 

 The radial current is led into the disk A through the tube F 

 and the wire G. The tube F passes through a central hole 

 in one of the pole-pieces of the electromagnet. 



The coils are shown at C x and C 2 . They each consist of 

 about 800 turns of fine wire having a resistance of approxi- 

 mately 315 ohms. The inside diameter of the coils is 2*0 cm. ; 

 the outside diameter is 4*0 cm.; and the thickness is 0*18 cm. 

 The coil Cj is cemented into a hard rubber ring so that it 

 may be taken out when a different disk and ring is employed. 

 The ends of the wire pass through two small holes in the ring 

 D. The coil C 2 is cemented inside the hard rubber cap H 

 which fits over the ring D. For better insulation there is a 

 thin sheet of mica between each coil and the disk A. The 

 two coils are connected in series in such a way as to double 

 the mutual inductance between the disk and coil. 



A rotating commutator, similar to that described by Rosa 

 and Grover*, was employed to reverse the radial current in 

 * Bulletin of the Bureau of Standards, i. p. 153 (1905). 



