Dr. E. Bouty on the Magnetization of Steel by Currents. 125 



The determination of d is, to be sure, less precise, since it 

 rests upon a single observation, that which refers to the 

 mother needle, and, besides, d is always a rather small 

 quantity; still, by multiplying observations and taking the 

 means, satisfactory results can be arrived at. 



Quantities of Magnetism. — The following results refer to 

 needles of 0*553 millim. diameter; the numbers of both 

 columns are expressed in arbitrary units : — 



Intensity of the current. Quantity of magnetism. 



3 hardly sensible. 



5 0-12 



7 0-51 



9 1-09 



12 , 2-11 



13-8 2-89 



15 3-35 



18 5*65 



23 11*96 



28 17-90 



36 23-00 



40 24-00 



50 25-90 



oo 28-90 



In order to represent better the course of the function m, 

 a curve can be constructed by taking the intensities for abscissae, 

 and the corresponding values of m for ordinates. At first con- 

 cave towards the positive ordinates, the curve then presents an 

 inflection-point corresponding to the abscissa 22 nearly, and 

 approaches asymptotically a parallel to the axis of the abscissae. 



These characters are identical with those of the curves which, 

 according to Rowland and Stoletow, represent the magnetizing 

 function of iron or steel*. The general features are every- 

 where the same ; and the resemblance is especially striking 

 when, opposite the preceding curve, we draw that found by 

 Rowland for Bessemer steel f. 



It is nevertheless expedient to examine if there is for tem- 

 pered steel a true magnetizing-function — that is, if the quo- 

 parallel to a given straight line A D. The line A D is perfectly known ; 

 as to the point C, its position on the ordinate CP admits an error, in 

 excess or defect, C c, whence results for D an error, negative or positive, 

 equal to B b. 



* This is the quantity of magnetism fi referred to unit volume and re- 

 garded as a function of the intensity of the magnetizing force. 



t Here is the Table which has served for tracing this curve • it is de- 

 duced from the original memoir published, in August 1873, in the 'Phi- 



