shuddemagen. — demagnetizing factors for iron rods. 235 



Discussion of Investigations on the Demagnetizing Factors. 



It was considered worth while to collate briefly the leading experi- 

 mental conditions which have been used in the determinations of N for 

 iron cylinders. Table XIV on the preceding page has therefore been 

 constructed from available data. 



It will be noticed that Mann used some very thick iron bars in the 

 first two of his experimental series. However, a given diameter re- 

 mained constant only throughout a single magnetization curve, say for 

 m = 5 ; after this the bar was turned down to a smaller diameter on 

 the lathe, so that m was thereby increased. If now the ballistically 



wo 



200 



suo 



1100 



400 500 600 700 



MAGNETIZING FORCE 3C 



FIGURE 17. 



Mann's magnetization curves obtained magnetometrically. The bars vary in 

 diameter from 2.370 cms. to 0.237 cm., while the length remains constant. 



obtained results of the present paper can be at all related to magneto- 

 metric experiments on similar iron rods, they would lead us to expect 

 that had Mann cut down his longest rod of 25.08 cms. from m = 50 to 

 m = 5, the values of N thereby obtained would not have agreed with 

 those which he did get by turning down the bar from m = 5 to m = 

 50. In fact the two sets of values for X, belonging to the two methods 

 "sawing off" and "turning down" respectively, would probably have 

 diverged more and more as m was decreased, the " turning down ' : 

 values for N being always less because the diameters of the bars of 

 this method are the greater, as carried out. 



As noted in the outline at the head of this paper, Mann found that 



