PROPERTIES OP IRON AT A HIGH TEMPERATURE. 
457 
This shows doubtfully the effects of magnetisation previous to heating, but, com¬ 
paring it with Table 10, it completes the proof that the asymmetry was in that case 
clue to the magnetising force, which had been stopped when the ring was non¬ 
magnetic. 
I have dwelt at length on these experiments because they show two things : first, 
that heating until the ring becomes non-magnetic does not clear the material of the 
magnetism when it is afterwards cooled ; second, that demagnetisation by reversal 
does not bring back the material to its virgin state, but leaves it in a state in which 
the induction is much less for small forces and greater for medium forces than a 
perfectly demagnetised ring would show. 
To return to the effects of temperature, Curves XX., XXI., and XXII. show the 
relation of permeability to temperature for magnetising forces 0'3, 4, and 30. 
It will be seen that they present the same general characteristics as the curves for 
wrought iron. The irregularities are due in part, no doubt, to the dej^endence of the 
observations on previous operations on the iron ; in part, to uncertainty concerning the 
exact agreement of temperature of iron and temperature of secondary coil. 
Whitivortlis Hard Steel. —This sample was supplied to me with the following 
analysis of its composition :— 
C Mn S Si P 
Per cent. 962 -212 -017 *164 -016 
The dimensions of the ring were exactly the same as the mild steel. 
The secondary coil had 56, the primary 101, convolutions. ' 
The resistance of the secondary and leads was '732 at 8° C. 
Experiments were first made with the ring cold, partly to show the changes caused 
by annealing, and partly to examine the behaviour of the virgin steel. 
The first series given in Table 24 was made on the virgin steel. The actual elonga¬ 
tions on the galvanometer are given, as they afford a better idea of the probable errors 
of observation. These shqw that for very small forces the first and second elongations 
are practically equal, but that for forces between 1 C.G.S. unit and 14 C.G.S. units 
the first elongation is very materially greater than the later elongations. 
The ring was now demagnetised, with magnetising forces ranging down to 0'0045, 
and the experiment was repeated, the results being shown in Table 25. Comparing 
them with Table 24, we see that the effect has been to reduce the inductions for low 
forces, as was the case with mild steel, and to render the kicks practically equal, 
whether they arise from the current first applied or subsequently applied. 
The ring w^as not now demagnetised ; the last current, giving a magnetising force 
35‘36, was removed, but not reversed, and a series of experiments made, the first 
reversal in each case being from the direction of the current of 35*36 last applied. 
The results are given in Table 26. 
MDCCCLXXXIX.—A. 
3 N 
