tn changing the Dimensions of Iron. 173 
bar 3-4 div., and that after the current was broken its magnetic 
intensity was found reduced from —1°3 (the permanent inten- 
sity previously given by 47° 25’, see preceding table) to 
~17. He then passed a current of 9° 55’, and this he found 
was sufficient, not only to remove the former minus polarity of 
the bar, but also to give it a permanent polarity of +'25, and 
yet to leave the bar with 6°6 of the elongation belonging to its 
previous minus rity. 
aking Joule’s observations while the current was passing 
5 
the current has been cut off. The discrepancies observa 
will, I think, be satisfactorily accounted for when we consider 
the nature of the magnetic actions taking place. When a bar 
experiences the inductive influence of a coil traversed by an 
have to withstand the opposing inductive influence of a greater 
humber of magnetic particles than the latter. This phenomenon 
will be diminished in the extent of its manifestation with an 
increase of the electrical foree, and will finally disappear when 
When the iron, after having been magnetized by the coil, is 
abandoned to its own retentive powers by cutting off the elee- 
trical current, the magnetism of the interior particles will suffer 
@ greater amount of deterioration than that 
- Wiedeman ae R. W. Wilson, “ Demagnetization 
n, Pogg. Ann. . 235; also W 
of Electro-Magnets,”” Amer. Nai Sci., 3d series, vol. iii, p. 346. 
