Constants of a Rectangular Galvanometer. 

 Total force due to AD and BC 



793 



oxri , 4i sin 6 , cos (f>i 

 = 2h cos ^> L = 2- J 



Fur. 4. 



Hence tlie total force at P due to the four sides of the 

 rectangle 



c% _ , • Tsin ^ cos </>j , sin 0„ cos ^"l 

 _ ^ - 4i ^ - + l J- ; 



which, remembering that 



j. d ± G ■ a c 



cos ^>] = -, cos <p 2 = 7 i sin C7J = 



— , sin 0o = — -j r 



and 



d 2 + ^? 2 , b 2 = c 2 + A' 2 , gives at once 



y_ 4*«* / 1 L 1 ) .... 



^^,^1^1^/cvr • • • w 



an expression which, when %=0, reduces as it should to 

 the value 



4/' 



^= Wc 2 + d 2 . 



§ 7. This value of $ may now be used to find the constant 

 of the " strip " galvanometer. If the current be assumed to 

 be uniformly distributed throughout the strip, and its value 

 per unit breadth of the strip be i, then the force at due to 

 an (dement of the strip of breadth dx at a distance ■>: from the 



