36 BELL SYSTEM TECHNICAL JOURNAL 



investigation (the "rotor," M) is wound with a magnetizing coil and 

 suspended by a fine quartz fibre in a second (induction) coil A. The 

 leads from the latter are connected in series with an adjustable re- 

 sistance R and a third coil B, inside of which is a small permanent 

 magnet (moment m) mounted below the rotor and connected rigidly 

 to it. A change in the moment of the rotor is produced by changing 

 the current in the magnetizing coil. This causes a gyromagnetic 

 rotation of the rotor and at the same time induces a voltage in coils A 

 and B. R is adjusted so that the current flowing is of such strength 

 that the field produced by it in B acts on the permanent magnet to 

 annul the gyromagnetic torque of the rotor. The magnetizing current 

 is alternated with a period equal to the natural period of rotation of 

 the rotor assembly and the final deflection 5 noted for various values 

 of R. R is plotted against 5 and its value, Rq, determined for zero 

 deflection b}^ interpolation. 

 Let 



La — — dJjdt 



be the torque due to the gyromagnetic effect. The current induced 

 in coils A and 5 by a change in the moment M of the rotor is 



i = EIR = (dMldt)(KAlR), 



where Ka is a constant of coil A. This current produces a torque on 

 the magnet w in ^: 



Lb = iniKn, 



Kb being a constant of coil B. When R = Rq, La — — Lb and 



dJ thKaKb 



P = 



dM Re 



The value of p is calculated by this formula after finding the values 

 of the coil constants, the resistance Ro and the moment of the perma- 

 nent magnet. Barnett has taken great care to eliminate various 

 errors caused mainly by the presence of undesirable fields such as the 

 earth's and by asymmetry and magnetostriction of the rotor. 



Experimental Values of g 



The results of gyromagnetic experiments are given preferably in 

 terms of g : 



g = (MIDilmcle), 



and are collected in Table III. Here a g- value of two means that 



