Magnetic Induction in Straight Iron Rods. 

 Table VII. 



493 



No. of 





I 





I 

 a ~ 2" 



specimen. 



d. 



2" 



a. 





d v 



4 



•982 



5-50 



595 



•458 



5 



•978 



7-46 



7-88 



•430 



6 



•986 



11-00 



11-50 



•506 



7 



•747 



6-48 



6-85 



•495 



8 



1-12 



1500 



15-60 



•535 



9 



112 



7-50 



7-97 



•420 



10 



100 



650 



6-97 



•470 



11 



•719 



6-50 



6-82 



•445 



12 



•772 



7-50 



7-92 



•545 



Mean of '. 



coli 



•48. 



From these tables it will be seen that equation (9) repre- 

 sents the real distribution with an accuracy of about 1 per 

 cent., a difference of 2 per cent, between observed and calcu- 

 lated values being very rare. 



The value of a in equation (9) seems to depend altogether 

 on the diameter (equivalent diameter if section is square). 



It was found that for all specimens of the same diameter 

 the difference between a and the half-length was constant. 

 This fact suggested that a might be determined by the 

 equation 



a=^+K^ (10) 



K x being a constant and d the diameter. The value of K x 

 in this equation as determined from the observations is '48. 



Table VII. gives the value for different specimens. 



The somewhat large variation from this value would indicate 

 that Ki was not constant in equation (10), but when it is 

 considered that its value is obtained by taking the difference 

 l_ 

 2 



tion of this kind is likely to be obtained. On the other 

 hand the variations are not regular, which would indicate 

 that it was constant. 



between a and — , which is small, it will be seen that a varia- 



It may be here noted that in the case of specimens Nos. 10, 

 11, and 13, the magnetizing force was obtained by using the 

 solenoid which was employed in measuring hysteresis loss 

 by the method above referred to. This solenoid is 13' 7 centim. 

 long, with a mean diameter of 3*03 centim. The length of 

 these specimens is 13 centim. The field was therefore by no 

 means uniform, but from fig. 5 it is observed that the distri- 



Phil. Mag. B, 5. Vol. 46. No. 282. Nov. 1898. 2 M 



