CHAP. XIII] TORQUE AND TRACTIVE EFFORT 



247 



current, this contraction of cross-section became so great at 

 one point that a deep depression was formed in the liquid, with 

 steeply inclined sides, like the letter V. 



In most cases of mechanical forces in a magnetic field, tin -< 

 forces and the resulting movements are due to the combined 



Stop 



Coil 



Core 



80, A trariivr electromagnet . 



1 . Two bun-bars and thoir 

 upport. 



action of longitudinal frnsims and transverse coin: > and 



not to one of these actions alone. I'm- instant , a loop of llexihle 

 wire, through which a large cum-nt is flowing, tends to stivteh 

 so as to assume a maximum opening, that is, a maximum 

 permeance of the magnet ie firl.l linked with it. This action 

 is due to both tin- l"ii-inidinal tension and the Int ssure. 



In such cases tin- m.-rhamVal forces an- hesi enmputed ly the 

 [M-inciple of virtual displae-inrn!> explained in the next article. 



