Intelligence and Miscellaneous Articles. 517 



times the diameter, is then equivalent to that of the rings ; it has 

 this advantage, that we can ascertain at any moment the real 

 magnetic condition of the metal, and demagnetize it so as to subject 

 it to fresh tests. 



The mean coefficient of magnetization diminishes very rapidly 

 with the ratio A of the length of the cylinder to its diameter, and 

 soon becomes of the same order as the coefficient f v relative to the 

 transverse magnetization. Further, the magnetization is propor- 

 tional to the intensity of the external field, within much more 

 extended limits. 



By forming short cylinders with packets of the same iron 

 wire as before, we have obtained as mean values in fields of 1 to 

 10 units : 



A. /• A 



12-3 3-40 0-13 



7-5 1-90 0-14 



5-0 1-20 0-14 



3-3 0-73 014 



Rectangular bars of soft iron gave in like manner for the mean 

 coefficients of magnetization/, f v / 2 , parallel to the three edges : — 



Dimensions. 



c. c. c. /. f v f 2 . 



9 1 1 2-0 0-15 



9 2 1 1-34 0-22 0-10 



9 2 2 0-88 0-15 



9 3 2 0-72 0-20 0-13 



Theory shows that in the case of infinitely long cylinders the 

 coefficient / for transverse magnetization is expressed by 



h 1 __ 0-159 



+ 2^~« r, , I \ , . 1 ' 

 '2wk 



H 1+ 'St) 1+ : 



and should be below 0*159 ; it will be seen that experiment gives 

 values near this limit, even with very short cylinders. 



A knowledge of these coefficients of magnetization is of particular 

 interest, as furnishing a correct means of calculating the effect of 

 the magnetization induced by the Earth in a magnetized bar, in 

 observations relative to the absolute measurement of the terrestrial 

 field. 



More generally, when a body is isotropic and of any given form, 

 there are three rectangular directions for which the magnetization 

 is parallel to the external field, with different coefficients/,/, and 

 / 2 ; these coefficients have the same properties as the coefficients 

 of magnetization of a feebly magnetic anisotropic substance. 



Suppose, for instance, that />/ and that the body is movable 

 about an axis parallel to the direction / 2 in a field whose component 



Phil Mag. S. 5. Vol. 21. No. 133. June 1886. 2 O 



