476 N. D. C. Hodges—Absolute Galvanometer. 
when F is the directive force of the current on a magnet of 
unit magnetic moment. 
The moment of the force F on the magnet is 
C (G, g, sin6 + G, g, sin? Q’ (8) + ete.) 
= sind C (G9, + G,g, Q! (0) + ete.) 
#=the angle between the axis of the coil and of the magnet. 
Hence C (G,9,+ Gg, Q,' (®+ ete.) = F. 
For the small angles through which the magnet need vibrate, 
this factor may be considered constant and equals the constant 
of the instrument, used as a tangent galvanometer, when the 
deflection is supposed equal to 90°. 
Let G,g, + G, g, Q,’ (0°) + ete. =K,,. 
‘Then F = CK,,. 
The value of C is obtained in the form 
ont) T 
"hesgea: . Se 
i 90 
To find the value of Kyo. the same current, if passed through 
the instrument used as a tangent galvanometer, will give 
of te ’ 
C= Ko tan p 
H T 2 e—t? Tt 
= = t* tan p 
_ if the value of Ky is known for any value of g, the deflec- 
tion, the constant of the instrument used in this other way is 
given by this formula. 
It is evident that the relative values of Ko for different 
values of the deflection of a tangent galvanometer may be 
found by repeated application of this process. 
vanometer would also apply. | 
Physical Laboratory, Harvard College, Feb. 12, 1879. 
