H. A. Rowland — Studies on Magnetic Distrihutio 





This distribution is not the same as that given by M. Jamin ; 

 but as his method is so defective, and his " normal magnet" so 

 indefinite, the agreement is sufficiently near. 



The surface-density at anv point of a maiinet is 



which, for the same kind of steel, is dependent only on -and-v 

 Hence in two similar magnets the surface-density is the same 

 at similar points, the linear density is proportional to the linear 

 dimensions, the surface integral of magnetic induction over 

 half the magnet or across the section is proportional to the 



irface dir 



j of the magnets, and the magnetic mc 

 the magnets. The forces at similar 





with regard to the two magnets will then be the ! 

 these remarks apply to soft iron under induction providing the 

 inducing force is the same, and hence include Sir William 

 Thomson's well-known law with regard to similar electromag- 

 nets ; and they are accurately true notwithstanding the approximate 

 nature of the formula from which they have here been deduced. 



Our theory gives us the means of determining what eflfect 

 the boring of a hole through the center of a magnet would have. 

 In this case R' is not much affected, but R is increased. Where 

 the magnet is used merely to affect a compass-needle, we should 

 then see that the hole through the center has little eflect where 

 the magnet is short and thick ; but where it is long, the attrac- 

 tion oti the com pass- needle is much diminished. Where the mag- 

 net is of the U-form, and is to be used for sustaining weights, 

 the practice is detrimental, and the sustaining -power is diminished 



