236 MEASUREMENT OF CURRENTS. 



A unifilar suspension in like manner would give 



8 + 8' 



HS 8 + 8' 

 cos 



The conditions of sensitiveness of the apparatus, in the case 

 of bifilar suspension, are the same as for a tangent galvanometer. 

 With unifilar suspension we have 



_ HS cos 8 



s c~ 



S = 



i + 8 tan 8 ' 



The absolute sensitiveness, which is proportional to the intensity 

 of the field and to the surface of the coil, is again a maximum 

 for zero deflection ; and the relative sensitiveness is a maximum 

 for 8 = cos 8, or about 8 = 40. 



857. The intensity of the current in the tangent galvanometer 

 is proportional to the horizontal component of the terrestrial field ; 

 for a movable coil, on the contrary, it is inversely proportional. A 

 combination of the two methods would thus enable us to get rid 

 of the action of the earth, and determine the intensity of the current 

 as a function of the dimensions of the two instruments and of the 

 directing couple of the suspension of the coil. 



If, as Kohlrausch* has pointed out, we pass one and the same 

 current I through a tangent galvanometer and through a movable 

 coil with bifilar suspension, then indicating by an accent the 

 deflection and the elements of the coil, and supposing all the 

 corrections for adjustment made, we shall have 



* F. KOHLRAUSCH. Pogg. Ann., Vol. cxxxvm., p. i. 1869. 



