. becomes 



and this is the ratio of the values of Q^'g at the ends of the 

 helix. When b is 12 inches, as in this case, we get the follow 



ng values of tl 



ns rati. 



:>■•- 











r= 



•05. 



•1. 



•15. 



•20. j 





CO. 





4-43 



•3494 



2-40 1 



2-20 1 



■4863 



•500 



To compare this with our experiments, let us plot Table 1 

 once more, rejecting, however, the end observations and con 

 pleiing the curve by the eye, thus getting rid of the error intr 

 duced at this point We then find for this r%tio, according 1 

 the different curves, 



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 shovf that r de- 

 creases, as we should expect it to do from the variation of ^. 



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

 mula (10) 



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

 Making 6=12, we have from this 



By experiment we find that the neutral point is, in all the 

 cases we have given in Table X, between 76 and SI inches, 

 which are quite near the points indicated by theory for the 

 proper values of r, though we might expect curve D to pass 

 through the point x=9, except for the disturbing causes we 

 have all along considered. 



Our formulae, then, express the general facts of the distri- 

 bution in this case with considerable accuracy. 



These experiments and calculations show the change in dis- 

 tribution in an electro-magnet when we place a piece of iron 



