AS A MEASURING INSTRUMENT. 



407 



magnetism, multiplied by the sine of the sum of two corresponding 

 angles of each series. We shall therefore have : 



If{n")=zMsin{n"-\-m") 



If{ri)= Msin (n' + m') 



If\n ) = Msin (n +m ) 



If (n t ) = Msin (n t -f- n, ) 



If (n„) = Msin {n„ + m„) 



If, on the other hand, the coils lie in the magnetic meridian, and 



we pass through them successively currents of the intensity I". I', I, 



I', I", which produce the deflections n", n', n, n n n in we shall have 



I"f (n") = 31 sin n" 

 I'f\n')z= 31 sinn' 

 If (n ) = 31 sin n 

 I l f(n l ) = 31sinn l 

 I /l f(n IJ ) — 31 sin n n 



By eliminating the unknown functions, we obtain from these two 

 series of equations the values of the intensities J", /'••••, correspond- 

 ing to the deflections n", n' , referred to the normal intensity /. 



W' r l' p r J\ 



Figure to illustrate Poggendorft 's method of measuring with the galvanometer. 



