528 



As an example may serve tlie case that (lie magnetic field is 



liomogeneons over ils entire height. We can then write f{H] = H. 



Then we obtain for tiie lateral pressure the well-known formula 



z — 1 \ ILll — Hll 

 and for the form of the string 



■ƒ■ 



4/ 



h=- I Hldl —--HI'' 

 2 P 



the length of the string being 2/. 



This last expi'ession represents the vertex-equation of a parabola. 

 In a homogeneous field the string takes the form of a parabola. 



In these and also in the following considerations we assume that 

 the longitudinal tension in the vertical string is everywhere the 

 same, and that the weight of the string itself may be neglected, 

 compared with its tension P. 



The formula given above may also be applied in cases where the 

 held, taken over the height, is not homogeneous. It may be applied, 

 if we can express the local field-intensity either in figures or in 

 a formula. 



In the string-galvanometer where the pole-pieces are pierced, we 

 can, as a first approximation, lepresent the intensity of field by the 

 line / (fig. 5). Over the length l^ corresponding to half the width of 



Fig. 5, 



