Mr. H. A. Rowland on Magnetic Distribution, 

 And if x is reckoned from the end of the rod, we have 



Q '' e= fK'7 6 " r( * +,r){1 ~ 26r6 + 62 " } ' 



When #=0, this becomes 

 6AL 



2tt 



e -r6(2-2e'' fi ); 



and when x=b } it becomes 



5—= e~ 2rb (I — 2e rb 4- e 2rb ) 

 2R'r € [l ** +6 h 



the ratio of which is 



(e-' 4 -l) ; 



353 



(10) 



and this is the ratio of the values of Q" e at the ends of the helix. 

 When b is 12 inches, as in this case, we get the following values 

 of this ratio : — 



r = 



•05. 



]. 



•15. 



•20. 



•30. 



GO . 



-Ke- r *-l) = 

 -2 



•2256 

 4-43 



•3494 



2-86 



•4173 

 2-40 



•4546 

 2-20 



•4863 

 206 



•500 

 200 



e-rb-Y 



To compare this with our experiments, let us plot Table X. once 

 more, rejecting, however, the end observations and completing 

 the curve by the eye, thus getting rid of the error introduced at 

 this point. We then find for this ratio, according to the different 

 curves, 



B. C. D. 



2-1 23 32 



It is seen that these are all above the limit 2, as they should 

 be — though it is possible that it may fall below in some cases, 

 owing to the variation of the permeability. As the magnetiza- 

 tion increases, the values of the above ratio show that r decreases, 

 as we should expect it to do from the variation of fju. 



To find the neutral point in this case, we must have in for- 

 mula (10) 



e 2 ™=2e r6 — 1, 



where x is the distance of the neutral point from the end. Making 

 6 = 12, we have from this : — 



Phil Mag. S. 4. Vol. 50. No. 332. Nov. 1875. 2 A 



