Determinations of Magnetic Susceptibility. 



441 



than in the case of the latter. The values obtained of the maximum 

 magnetisation of these wires are as follows : — 



1. The dark wire 



2. The bright wire 



3. The steel pianoforte wire 



4. The glass-hard-tempered 



wire 



The curve (a) in the Diagram III shows that the maximum 

 residual magnetism of the tempered steel wire is considerably greater 

 than three-fourths of the total magnetism of which it is a residue ; 

 whereas in the case of the soft iron wires the maximum residual 

 magnetism is only a small fraction of the total magnetism. 



Passing now on to the curves in the Plate 14, no more words are 

 perhaps necessary to explain them, because the explanations given of the 

 curves in the Plates 11, 12, 13 will exactly apply to the corresponding 

 curves in the Plate 14, if we substitute the words "Magnetic Suscep- 

 tibility" for "Intensity of Magnetisation." By the corresponding 

 curves is meant the curves which are marked by the same letters, 

 such as (a), (5), &c, in the diagrams designated by the same numbers, 

 such as I, II, &c. 



With regard to the results for the magnetic susceptibility, it may be 

 remarked that the results of the preliminary experiments not given in 

 the paper, showed that the susceptibility of any one of the wires is 

 different according to different circumstances under which it is placed, 

 that is to say, that there is, for each magnetising force, an infinite 

 number of values for the susceptibility corresponding to an infinite 

 number of amounts of pull to the applications and removals of which 

 the wire might have been subjected (though this appears to cease to be 

 the case when the magnetising force exceeds a certain value, that is, 

 when the wire begins to lose its retentiveness), not to speak at all of 

 the different values for the susceptibility the wire has at any given 

 stage of its history, according to the different amounts of a permanent 

 pull to which the wire may be subjected. Hence it is evident that we 

 should have a precise knowledge of the history, past and present, of 

 the body whose susceptibility we wish to determine ; and this is the 

 very reason why the experiments were made on the wires under 

 definite circumstances. The two sets of the values for the suscepti- 

 bility of each wire, one for the case " On," and the other for " Off," 

 given in the corresponding table and represented by the curves, are, 

 therefore, those corresponding to that particular circumstance under 

 which the wire was experimented on. The magnetic susceptibility of 



