Elasticity of Ferromagnetic Substances hy Magnetization. 465 



From the change of depression we may calculate the ratio 

 of the change of elasticity to the modulus itself. The depres- 

 sion due to the suspended weight as well as to its own weight 

 in an unmagnetized bar is given by the approximate formula* 



where /, a, b are the length, breadth, and thickness of the 

 bar, T and W the suspended weight and the weight of the bar 

 itself respectively, d and W refer to the part of the bar 

 lying between two fulcrums. The obseryed change of de- 

 pression diyided by this depression is the ratio in question, 



that is, 



SE 

 E 



Some of the results of our calculation are given 



in the following table. In the calculation the effect of 

 the weak spring stretching the thin copper wire was 

 corrected for. 



1 



H/T+fW. 



329 gr. 



829 gr. 



1349 gr. 



1849 gr. 



5869 gr. 



20 



164xl0- 2 



0-77 Xl0~ 2 



0-50 X10~ 2 



0-47X10- 2 



0-44X10- 2 



30 



2-79 



1-47 



1-09 



1-08 



0-88 



50 



315 



1-84 



1-35 



1-28 



1-16 



100 



3-36 



1-92 



1-48 



137 



1-28 



250 



3-40 



1-93 



1-51 



1-40 



1-32 



400 



340 



1-93 



1-51 



1-40 



1-32 



These numbers show that the value of -^ becomes greater 



as the field is increased, and that it becomes less as the weight 

 is increased. 



Fii 



5. Steel.— The general character of the change of depression 

 is similar to that of soft iron, as given in fig. 5 ; but the 



* Clebsch's Elasticitcit, p. 37-5 ; Winkelmann's Physik, i. p. 266. 



