140 Dr. F. Auerbach on the Passage of 



and 



g= /'" A x (4b) 



w(iv + w A ) 



This equation can be readily verified if we pursue the extra 

 current which arises at the closing of a known current, if the 

 current deflects a magnetic needle of known moment, and if, 

 besides, the horizontal component of the intensity of the earth's 

 magnetism is known*. 



In regard to practice it is at all events most convenient, 

 whenever work is performed, whether momentary or lasting, 

 to admit an alteration of the resistance. 



Accordingly the resistance of an iron wire in the first moment 

 after the closing must be greater, in the first moment after the 

 opening it must be less, than during the rest of the time that the 

 current lasts. For then the molecular magnets, in consequence 

 of the directing force of the current, shift into a position more 

 or less approximating to the circular arrangement when the 

 current has to perform work in relation to the direction-force 

 of the molecules. Here the molecules return more or less into 

 their natural position ; the direction-force therefore does work 

 in regard to the current. With this the observations are in 

 complete accordance. 



As soon as that actual energy which the molecular magnets 

 receive from the rotating force of the current is entirely con- 

 verted into potential, the current has no more work to perform 

 with respect to the direction of the molecular magnets. Hence 

 we could not but conclude that the resistance would now take 

 its true value, corresponding to the iron wire at rest internally 

 (or in a determined thermal motion), if we had not to bear in 

 mind that through the action of the rotating forces exerted by 

 the current the internal state of the iron (as may also be ima- 

 gined) has become different, and remains so till the current is 

 interrupted. Accordingly the iron might possess two different 

 resistances, of which one only, viz. that of the circularly mag- 



* That even in the case represented by M. Colley (e variable) equa- 

 tion (2 a) is not applicable may be inferred from its leading to a contra- 

 diction. For M. Colley arrives by correct conclusions at the equation 

 (corresponding - to eq. 4 b) 



w 



which cannot be true, since for e indefinitely small it yields 



e de • , j n 2ede 



q— instead of g= : 



w w 



while if in this case also, as above, we make use of eq. (3), it brings us to 

 the last-mentioned, the true equation. 



