Dr. E. Bout j on the Magnetization of Steel by Currents. 133 



The following Table shows the values found for r with needles 

 of 0*553 millim. diameter: — ■ 



Current. 



P- 



r 





Difference. 



Weight. 











Observed. 



Calculated. 



i 





8-45 



8-573 



7-290 



6-399 



+0-891 



2 



10-56 



4-255 



3-590 



3-932 



-0 342 



1 



1179 



3-819 



3-058 



3-237 



-0 179 



4 



12-81 



3-293 



2-765 



2818 



-0083 



1 



1439 



3-089 



2 641 



2-438 



+ 0-203 



2 



15-25 



3000 



2271 



2-279 



-0-008 



1 



1727 



2-409 



2-086 



2031 



+ 0-077 



1 



1S-75 



2073 



1-727 



1-877 



-0150 



2 



20-28 



2167 



1-834 



I 773 



+0061 



6 



23-56 



1-919 



1-622 



1-623 



-0001 



5 



26-50 



1-624 



1-399 



1-539 



-0150 



6 



31-32 



3-581 



1-374 



1-442 



-0-078 



7 



36-24 



1-506 



1-390 



3 -400 



— 0-010 



2 



41-79 



1-462 



1-331 



1-368 



-0037 



3 



68-68 



1-343 



1-340 



1-297 



+0043 



; 



The numbers of the last column indicate the number of 

 needles employed for the determination of the corresponding 

 value of p. In order to avoid any systematic error proceeding 

 from the calculation of r, for different intensities of the cur- 

 rent, needles of different lengths were employed, the centre of 

 which was always placed at a fixed distance from the galvano- 

 meter-needle*. 



The numbers in the fourth column were calculated by the 

 formula 



= 1-2619 + 



0-3)' 



(3) 



with log a = 2*18355 ; x represents the intensity of the current. 

 The same formula suits very well to express the ratio r for 

 thicker needles, 0*687 and 0*957 millim. in diameter for in- 

 stance, on condition of making a — aD, a being a constant "j*. 

 A similar formula also suits for the Bessemer steel investigated 

 by Rowland, except for the highest intensities; the ratio r 

 then presents a notable augmentation, observed also in some 

 of my experiments, and to which we shall revert by-and-by. 



We have already seen that, properly speaking, there is no 

 function of permanent magnetism for tempered needles of dif- 



* For this the needle under experiment is kept at the bottom of a tube 

 closed at one end, which fits with friction into the magnetizing helix. 

 T his tube is divided into half-millimetres ; and its position is regulated 

 b y means of a fixed mark traced upon the tube which carries the helix. 



t {This empirical formula succeeds very well for needles of from 045 to 

 1-50 millim. steeped at a dull red-heat, but is far from being general. 



