Theory of Electromagnetic Action. 453 



4^ { f ** HdB - J P 2 (HdB + BdH) | ; 



-^(area P Q S R-J area N Q S R P M). 



47T 



The second area of course vanishes when Q coincides with P, 

 as it does w T hen the curve forms a closed cvcle. 



that i 



is, 



Fig. 2. 



6 8 



10 12 14 16 18 20 22 24 

 Magnetizing Force, H. 



28 30 32 



It is interesting to apply this result to an actual curve of 

 magnetization in iron (fig. 2). For all points on the curve 

 up to a little distance beyond P, the total energy given to 

 the medium in producing the corresponding magnetization 

 exceeds the electrokinetic energy, but for all points further 

 from the origin the electrokinetic energy exceeds, and for 

 points on the upper flat part of the curve very greatly exceeds, 

 the energy given out to the medium by the battery. [The 

 point P at which OP is a tangent to the curve marks the 

 point at which the energy given out to the medium and the 

 electrokinetic energy are increasing at the same rate, the 

 former below that point is increasing faster, above that point 

 slower than the latter.] 



We are forced to conclude that for every series of mag- 

 netization steps from zero up to a certain point energy is 

 given to the medium, and for every series from zero up to any 

 further point the medium furnishes the balance of energy 

 required for the electrokinetic energy. In every small step 

 below P a balance of energy, over and above the electro- 

 kinetic energy, is given to the medium ; for every small step 



