the Galvanic Current through Iron, 143 



magnetizing force varies considerably with the thickness ; for 

 it is 



P = c 1 1 1 -js idr all dd>. 

 Jo Jo Jo d 



Integrating, and using the equation 



H 



w k + z±n l 



IT 



d- 



in which / signifies the specific resistance of iron, we get for 

 the magnetic moment : — ■ 



^ const, Rid , A , /A 



U>k 



' 72 



ird 



where $(d) is a complete function^of d, slowly varying as d 

 varies, and in the same direction, and ^(l) is a function of I 

 which is of no consequence here. For larger values of I, at 

 least if that of d is not too great, we can so arrange that w^ 

 may be neglected ; we then find : — 



K= const. HuPMd) . f(0- 



4/7 

 But even when d is so great that conversely -^-j 1 can be neg- 



d 2 



lected against w k , still 



K= const. Kdcj>(d) . ty(l), 

 while yet, as mentioned, the longitudinally magnetic moment is 



K ; = const. MW d%Q) • 



As the expression of the work done by the current in the 

 rotation of the molecular magnets, an extra current occurs at 

 the closing of the principal current, as we have seen, or, as it 

 was expressed, a passing augmentation of the resistance. If 

 the wire has been previously magnetized longitudinally, and 

 is still in that state at the closing of the principal current, the 

 rotation by the latter is of course much less. From this we 

 might at first be inclined to conclude that the work also is less, 

 which would be contradicted by the observed fact that the 

 extra current is in this case more intense. But we must bear 

 in mind that the rotation is smaller in amount because the lon- 

 gitudinally magnetizing force holds back the molecules more 

 strongly than the direction-force, which alone, in the first case, 

 counteracted the force of the principal current, but the other 

 factor of the product representing the work, the longitudinally 



