RESEARCHES IN MAGNETISM. 
561 
§ 42. Several experiments with other pieces of iron wire, first annealed and then 
hardened by stretching, have fully confirmed the results of the preceding paragraph. 
Plate 61, fig. 19, shows the relations of induced and residual magnetism, and of their 
ratio, to magnetising force in another piece of stretched iron wire, which was much 
more strongly magnetised than the wire in the former example. Here the ratio, after 
touching a maximum of 0‘6 with >§ = 9, fell to 0'32 when the magnetising force was 
raised to 9 2. 
Other experiments on the same subject will be found below in §§ 109-112, where 
the influence of stress on the ratio of residual to induced magnetism is considered. 
§ 43. My experiments were better adapted for finding the proportion of residual to 
temporary magnetism when the magnetisation was moderately strong than when it 
was very feeble. So far as can be judged from the curves and figures given above, the 
ratio is initially zero, that is to say, the earliest developments of magnetism, induced 
by a magnetising force rising from nothing, are entirely temporary, and disappear 
altogether when the force is withdrawn. But these experiments are inconclusive on 
this point, though they show distinctly that, in any case, very weak magnetisa¬ 
tion is very slightly retained when the magnetising force is withdrawn, even by 
specimens of iron which will retain as much as 90 per cent, of stronger magnetisation. 
In steel the absence of retentiveness at low magnetising forces is still more marked. 
It is clear from this that if we are to ascribe retentiveness to a frictional sticking of 
the displaced molecules, we must complicate the hypothesis by believing that all or 
some of the molecules have a certain range of possible displacement within which 
this friction does not act, or that some of them are free from frictional retardation. 
§ 44. Ratio of Residual to Induced Magnetism in Steel .—Corresponding observations 
were made on pianoforte steel, in the three states already mentioned, namely, in the 
normal commercial temper, annealed, and glass-hardened by sudden cooling. The 
wires tested were in each case 078 mm. diameter and about 30 centims. long. 
For pianoforte steel in its normal temper we have the following values of induced 
and residual magnetism for a graded set of values of .§. The ratio here passes a 
distinct maximum, and (in conformity with what has just been said) is, in the early 
part of the experiment, exceedingly small. The following are the actual magneto¬ 
meter readings, corrected for the electromagnetic action of the magnetising solenoid. 
To reduce them to they have only to be multiplied by 6 - 06. 
