Mr. Wheatstone 07i Electric Induction. 59 



miles. o 







no 6i 



220 12 



330 18 



440 23i 



550 28 



660 31 



Exp. 7. One end of the 660 miles of wire was now allowed to 

 remain constantly in contact with one of the poles of the battery ; 

 but the galvanometer was successively shifted to different distances 

 from the battery. The strength of the current was now shown to 

 be inversely as the distance of the galvanometer from the battery, 

 becoming null at its extremity, as shown in the follov.ing table. The 

 first column shows the distance from the battery at which the gal- 

 vanometer was placed, and the second column the corresponding 

 deflection of the needle. 



miles. o 



Near the battery .... S'd^ 



110 31 



220 25 



330 15 



440 12 



550 5 



660 



The deflections of the needle of the galvanometer employed in 

 these experiments were, when they did not surpass 36°, very nearly 

 comparable with the force of the current. This I ascertained in the 

 following way. I took six cells of the small constant battery de- 

 scribed in my paper " On new Instruments and Processes for deter- 

 mining the Constants of a Voltaic Circuit," printed in the Philo- 

 sophical Transactions for 1843, and placed in the circuit formed of 

 the 660 miles of wire, the earth, and the galvanometer, successively 

 1, 2, 3. 4, 5 and 6 cells. Leaving out of consideration the resist- 

 ances in the cells themselves and in the earth, which were very in- 

 considerable in comparison with that in the long wire, the force of 

 the current should be aj)pi-oximately proportionate to the number 

 of the elements ; and since the deflections of the needle nearly indi- 

 cated this proportionality, as the following table will show, it may 

 be assumed that the force of the current, when the deflection of the 

 needle did not sjurjiass 36°, nearly corresponded with the angular 

 deviation. 



cell. 



1 6 



2 14 



3 19 



4 28 



5 32 



6 36 



