4 ELECTRICAL MEASUREMENTS 



on the measured value of the current of the unavoidable de- 

 partures from the assumed conditions. 



In absolute electrical measurements this part of the work often 

 calls for mathematical ability of a high order. 



The Helmholtz Galvanometer. In this instrument the needle 

 is suspended on the axis midway between two equal coils, whose 

 distance apart is equal to their radius. 



FIG. 3. Helmholtz tangent galvanometer. 



The reason for this construction is that it renders the field in 

 the needle swings very uniform, so that the correction for 

 the finite length of the needle is much reduced. 



' arrangement of coils is frequently employed in other 

 instru: 8 where a uniform magnetic field is desired. 



bsolute galvanometers depend for their directive force 

 lonzontal component of the local field at the place where 



