202 



PROCEEDINGS OF T11K AMERJl '. 



This, bowever, is doI at all the case, and the actual tart- emphasize 

 the fallacy of considering the magnetization in long iron rods, when 

 not completely saturated, as even approximately uniform. As will ap- 

 pear from the results obtained in this investigation, the values of .V 

 are not far from being constant below />' = 10,000, and they are of the 

 order of magnitude as those found by Du Bois from Bwing's cur 

 although always somewhat smaller. But let us now find what tl 

 .V-\alut's wmild he if uur various rods were really uniformly magne- 

 d. In other words, let us find the position of K of the straight line 



3000 



2000 



YI 

 TV 



3. 



<♦_ 1500 vn 



o 



!3 1000 



mb 



vm 



500 £ 



a 



Centre 22 20 18 16 14 12 10 8 



Figure 4. 



end 



Lamb's curves showing the change in permeability along an iron rod. The 

 distances along bar arc given in inches. 



< >K in Figure •">. Our rod has the length L and diameter />, so that 

 uniform magnetization would mean - | /> 2 "/ units of free positive 

 magnetism on one end of the rod and the same number of negative 

 units on the other end. If L is large compared to />, we may regard 

 the demagnetizing field-intensity //, I i >r XI) at the centre of the rod 



aused by a Bingle point-pole of strength -~( ) 1 at a distance 

 of I. 2 units of length from it. Then 



