236 Mr. Albert Griffiths : Some 



I made another attempt at a theory, which, with the help 

 of sufficient hypotheses, gives results agreeing to some extent 

 with the facts. 



For simplicity, initially, the bismuth spiral will not be 

 considered as forming part of a Wheatstone bridge. 



It is very probable that when the bismuth wire is put in 

 a magnetic field the ultimate particles, crystals or molecules, 

 will become magnetized. The stronger the field the stronger 

 will the magnetization be. If now an alternating current be 

 sent along the wire, the magnetized particles will take up 

 forced oscillations. 



Let e=eiCosj?t represent the E.M.F. acting at the ex- 

 tremity of a bismuth wire. 



For simplicity, let us confine our attention to one particle 

 of bismuth. Let u = any displacement of the particle caused 

 by the alternating current ; then, approximately, the oscilla- 

 tion of the particle will be represented by 



u + ku + ?i 2 tt = E cos pt; (1) 



where k depends on friction and damping, and n =mm rfr ? 



T being the time of oscillation of the particle. T will depend 

 on the degree of magnetization of the particle, on the strength 

 of the field, and on the ultimate structure of the bismuth. 

 A solution of (1) is 



E sin e , . . , as 



w= "7F~ cos( ^"~ e) ' (2) 



where , ph ,„ 



tane=-/- — -„ (3) 



nr—p* ' 



IT 



Let e = ~ — « ; then from (3), 



<}1p __ /p2 



tana= -7* ( 4 > 



Equation (2) may now be written 



Ecosa . ,- . , x /c . 



w =— ££— sin (i>* + a ) (5) 



The movement of the particle will cause an E.M.F. along 



the wire ; if the amplitude of the oscillation be small, the 



du 

 E.M.F. produced will vary approximately as j- 



From (5), 



du E cos a. t . . \ 



