228 



MR J. C. BEATTIE ON THE 



A series of five experiments was made with each field strength. In 1st, 3rd, and 5th 

 E L M D was open, in 2nd and 4th E L M D was closed.* The average of the first three 

 was then divided by that of the 2nd and 4th. 



Next, the resistance of the bismuth plate was measured when the electro-magnet was 

 on. A current was sent by A in the direction A L E D M A, or vice versa, and E and D 

 were joined to the galvanometer ; four readings were taken — the resistances of the copper 

 wires L E, M D and of the short wire L M — the total being of the same order of magni- 

 tude as that of the bismuth plate. These measurements were made at the beginning and 

 end of each series of five experiments. 



Let C be the transverse current when E L M D is open, let S be the resistance of the 

 shunt ELMD, n that of the bismuth plate. Then theoretically we have 



C 



Current when ELMD is open 

 Current when E 1/ M D is closed 



c/n 



1/n+lls 



i+? 



But since we have measured n and s directly, we can calculate 1 + " ; the calculated 

 and the observed values will agree, if the transverse effect is of the same nature as the 

 current obtained from a cell of constant electromotive force. 



The following are some of the results obtained : — 



Plate (Ia). 



Length, 



Breadth, 



Thickness, 



5-63 



2-9525 



0T94I3 



cm. 



This plate was quickly cooled in casting ; the temperature of the room was in all the 

 experiments about 15° C. Made from first supply of bismuth. 



Plate (Ib). 



Length, .... 



Breadth, .... 



Thickness, .... 



Slowly cooled. Made from first supply of bismuth. 



6-045 



2-58 



0-12235 



cm. 



* The galvanometer reading obtained in this case, divided by the strength of the primary current, is called in 

 the results the shunted transverse. 



