196 Dr. E. Bouty on the Magnetization of Steel by Currents. 



placed perpendicular to the magnetic meridian. The coil is 

 mounted on four rollers, and can be removed at pleasure ; it 

 carries an index, which slides along the rail upon a divided 

 rule, the zero of which coincides with the axis of rotation. By 

 an appropriate arrangement the bars are kept exactly in the 

 axis of the coil. 



It has been verified that the deflection produced by a bar of 

 50 centims. length is exactly proportional to the cube of the 

 distance of its centre from the needle as soon as that distance 

 exceeds 2 metres: in general a much greater distance was 

 taken. 



Under these conditions I found that, for suitably selected 

 values of A and B, formula (1) will always represent the mag- 

 netic moments exactly, provided that all the bars, innocent of 

 previous magnetization, be magnetized in identical circum- 

 stances. It applies to the temporary as well as the permanent 

 magnetization, to bars of soft iron as well as to bars strongly 

 hardened, and whether one magnetizes to saturation or excites 

 the coil with a current of constant intensity too feeble to 

 saturate. 



The following Tables are intended to show, in some examples, 

 the degree of accordance between experiment and the for- 

 mula* : — 



Bars saturated, 



7 millims. in diameter 



, not hardened. 



Length. 



Temporary magnetization. 



Permanent magnetization. 



Observa- 



Calcula- 



Differ- 



Observa- 



Calcula- 



Differ- 





tion. 



tion. 



ence. 



tion. 



tion. 



ence. 



centim. 















50 



0-75 



0-758 



-0-008 



0056 



0074 



-0018 



7-2 



2-13 



2062 



+0068 



0-187 



0222 



-0035 



9-8 



412 



4-368 



-0-248 



0-469 



0547 



-0-078 



12-4 



713 



7852 



-0-722 



0-845 



1-068 



-0-223 



15-0 



12 54 



11-896 



+ 0-644 



1-726 



1-693 



+0-033 



19-8 



20-25 



20-358 



-0108 



3-440 



3517 



-0077 



25 



3019 



30260 



-0070 



6-328 



6-847 



-0-519 



300 



3772 



40-087 



-2-367 



10-91 



10-524 



+ 0-386 



34-5 



48-96 



49-037 



-0-067 



15 IS 



14-812 



+ 0-368 



400 









21-81 



2181 



0000 





A —4081 B,— l . 



A — 2 



34, B — 



1 





1 ' l 7142 







17-857 



* I think it expedient to apprise the reader that the numbers represent- 

 ing-, in arbitrary units, the measured magnetic moments in this section are 

 always evaluated with the same unit, which is several hundred times as 

 great as that made use of in the preceding sections. As the corresponding 

 experiments were made, the one series at Rheims, the other at Paris, the 

 data for establishing the exact value of the ratio of the two units are 

 wanting. 



