736 Dr. S. P. Thompson and Mr. E. W. Moss on the 



chosen for the calculation of the self-demagnetizing force 

 and deduction of the self-demagnetizing factor, except for 

 the very short rods in which lesser values of £B were alone 

 available. 



Fig. 2 gives as the final result the curve exhibiting the 

 values of the self-demagnetizing factors found, for rods of 

 different lengths, the corresponding values found by Du Bois 

 and by Biborg Mann being added for comparison. 



It will be seen (1) that our values are throughout lower 

 than those found by either of these experimenters ; (2) that 

 we have carried the determinations down to shorter rods 



Table I. — Demagnetizing Factors for Cylindrical Bars. 







Demagnetizing Factors. 





Cylinder. 









I 









Ellipsoid 



1 









of 



d' 



V Area 



Du Bois. 



Eiborg 



Mann. 



Thompson 

 & Moss. 



Eevolution. 



2-66 



30 







1-2 





3-55 



40 



... 





083 





4-44 



5-0 







0-618 





50 



5-64 





0-6800 



0-53 





5-34 



60 







0-483 





666 



7-5 





... 



0-3518 





8-86 



10-0 







0-233 





100 



11-28 



0-2*i6 



0-2550 



0-198 



0-2549 



1067 



12-0 







0-18 





13-3 



15-0 







0-1287 





15-0 



16-92 



01206 



01400 



0-108 



0-135 



17-72 



20-0 







00826 





200 



22-56 



00775 



008975 



0-069 



00848 



250 



28-2 



00533 



0-06278 



0-049 



00579 



266 



30-0 







00438 





30-0 



33-84 



00393 



004604 



0-086 



0-0432 



35-6 



40-0 







0-0255 





400 



45-12 



00238 



002744 



0-0223 



0-0266 



N.B. — Figures in italics are values got by interpolation. 



than those examined by either of them ; (3) that the dis- 

 crepancies between their results and ours are smaller as the 

 dimension-ratios are larger. 



The fact that our values are throughout lower than those 

 of Du Bois and Biborg Mann is doubtless due to the cir- 

 cumstance that they used a magnetometric method, whilst 

 we have returned to the ballistic method of Ewing. The 

 values of J which they employ are the mean values deduced 



