798 



Mr. A. Ferguson on the Construction and 



turn is given by putting x = 5, c = 20, d%='01 in equation (iii.) 

 above, giving 



^ = 3W0' approximately - 



§ 13. Consider now the method of correction of the value 

 cf the galvanometer constant due to the sides of the square 

 not being quite true. We shall consider only the case in 

 "which one of the sides of the square is in error by an 

 amount x. The result may be readily extended. 



Fig-. 7. 



The force at due to unit current in the single turn of 

 wire ABCD 



ri 2 sin 45° 2 sin 45° , sin 45° 

 c c c 



sin (45 f 8) , 1 /. /, , . n >. 

 H *— / + (sin 6 X + sin 2 ) 



+ ^- + r(sin^i + sin^ 2 ). • • ■ (iv.) 



Also 



^2.0 V2.c' b 



tan (j> = cf> = ^-, 



sin 5=8 



.y 



•2' 



-»/r = 45 — 8. 



y = «r sin ^ = x sin (45 — 8) = Sc^2, 



