276 Mr. N. D. C. Hodges on a new Absolute Galvanometer. 



where 



0=9O°-0, 



Then 



F=CK 90 o. 



Substituting this value of F in (3), we get the expression 

 for C ; 



Q= e-t\ _T_ . 



Cj J^90° 



To find the value of K 90 o, any of the ordinary experimental 

 methods may be used ; or, if the constant for any value of <£ 

 is known, when the same coil and magnet are used as a tan- 

 gent-galvanometer, it might be obtained as follows : — Having 

 a constant current, get its value in terms of K<p and the tan- 

 gent of the deflection, and then in terms of the quantities in 

 formula (4). 



T 



C = j^j tan <j> ; 



n_t 2 -tl T 

 t\ K 90O ' 



t\ tan0' 



It is evident that the relative values of K<p for the different 

 values of the deflection of a tangent-galvanometer may be 

 found by a repeated application of this process by the use of 

 currents of different strengths. 



t\ tan $ ' 



t 2 2 tan fa 



Kg __ tancft ?-t\ t\ 

 •'X ?1 tan^ t\ ' e-fl 



■^90° — ■ • 



Physical Laboratory, Harvard College, 

 Cambridge, U. S. A., March 1, 1879. 



