Mr. H. A. Rowland on Magnetic Distribution. 357 



purchased. These were wound uniformly from end to end with 

 one layer of quite fine wire, making 600 turns in that distance. 

 In finding X from Q" e , the latter was divided by 47rAL, except 

 at the end, where the end-section was included with AL in the 

 proper manner, x was measured from the end of the bar in 

 inches. 



Table XI. 



Iron Electromagnet. 



x= distance 



Qe. 



4ttX. 



47T\. 



Error. 



from end. 



Observed. 



Observed. 



Computed. 







22-5 



411 



33-9 



-72 



12-6 



251 



26-9 



+ 1-8 



2 



3 

 4 

 5 



6 



19-3 



19 3 



18-9 



-0-4 



120 



120 



117 



- 3 



6-6 



66 



M 



+ -5 



3-9 



3-9 



40 



+ -1 



29 



29 



17 



-1-2 



4tt\ = 42. 



The observations in Table XI. are the mean of four observa- 

 tions made on both ends of the bar and with the current in 

 both directions. 



The agreement with the formula in this Table is quite good ; 

 but we still observe the excess of observation over the formula 

 at the end, as we have done all along. Here, for the first time, 

 we see the error introduced by the method of experiment which 

 I have before referred to (p. 266) in the apparently small value 

 of 47rX at x='75. 



On trying the steel bar, I came across a curious fact, which, 

 however, I have since found has been noticed by others. It is, 

 that when an iron or steel bar has been magnetized for a long 

 time in one direction and is then demagnetized, it is easier 

 to magnetize it again in the same direction than in the opposite 

 direction. The rod which I used in this experiment had been 

 used as a permanent magnet for about a month, but was demag- 

 netized before use. From this rod five cases of distribution were 

 observed : — first, when the bar was used as an electromagnet with 

 the magnetization in the same direction as the original mag- 

 netism; second, ditto with magnetization contrary to original mag- 

 netism ; third, when used as a permanent magnet with magnetism 

 the same as the original magnetism ; fourth, ditto with magnetism 

 opposite ; and fifth, same as third, but curve taken after several 

 days. The permanent magnetism was given by the current. 



