160 Dr. W. F. G. Swann on the Magnetic. Field produced 



The Results^. 



The following tables show the results obtained in the main 

 experiments. The third column represents the deflexion 

 observed on discharging the central plate of the apparatus, 

 and the fourth column the values calculated in the above 

 manner. is written when the deflexion is less than 0'5 

 division. Such very slight deflexions as were observed are 

 doubtless due mainly to alterations of zero due to incomplete 

 astaticism of the galvanometer-needle, to lack of compensation 

 of the two coils as far as fluctuations of the earth's field are 

 concerned, and to residual electrostatic effects. There is 

 obviously no evidence of any appreciable deflexion ; the very 

 slight irregular deflexions observed are hardly to be wondered 

 at, in view of the facts that the galvanometer had a time of 

 swing of 11 seconds, the scale was 3 metres away, and the 

 central plate was charged to 4000 volts. 



Continued repetition of the experiments seemed unneces- 



sary. 



as the observations below were taken after much 



experience with the apparatus. The main part of the work 



Table I. 



Experiments performed on July 20, 2.40 a.m. to 3.40 a.m. 

 iEther drift vertical. ^ = 11*4 seconds. 



Central plate charged positively. 



Speed 



Potential of 



central plate. 



Volts. 



Deflexion 



Deflexion 



revs. 

 per miu. 



observed. 



calculated. 



810 



+4000 



10-4 



810 







10-4 



800 



-2 10-3 



800 



1 -3 



103 



800 







103 



800 



-1-5 



103 



800 



+0-5 



103 



800 



-4* 



10-3 



800 







103 



800 







1 



10-3 



Central plate charged negatively. 



Speed 



Potential of 



i 



l 



Deflexion! Deflexion 



revs, 

 per min. 



central plate. 

 Volts. 



'observed. 



calculated. 



810 



-4000 



+2 



10-4 



740 



... 



4-2-5 



9-5 



740 





+2 



9-5 



750 









9-6 



760 









9-8 



740 





+1 



9-5 



720 





4-0-5 | 9-2 



710 





4-2 



9-1 



The spot of light was unsteady when this observation was taken. 



t The calculated values of d x given in the tables are obtained on the 

 assumption that 7^=2-3. The value of k as measured, without taking 

 any precautions to prevent soaking, was higher than this. If the larger 

 value were used the calculated values of B r would be greater; it was 

 considered safer, however, in view of the possibility of soakage, to take 

 the value of h usually given in the tables for the kind of wax used. 



