CHANGE OF THE ABSOLUTE MAGNETIC FORCE BY HEAT. 1/!) 
ence of the upsetting' angles of these metals, was the different proportions of length 
and thickness ; another reason will appear further on (3427.). Two sets of results 
are entered in the chart of lines (marked N and ()), both of which present an im- 
portant indication. It may be observed, in the first place, of the results O, that 
ascending from 66° and then returning to nearly the same temperature, the cobalt 
seems to have gained a permanent increase of power of about 30 degrees of torsion 
force, the whole being about 380. This was ultimately referred to charge or coercitive 
power; for when, after the observations at 79°, the cube with the cobalt was turned 
round 180°, so as to reverse the ends as respects the magnetic poles, and then brought 
back into their first position and observed, the power of the whole seemed to have 
fallen, as is seen by the six results marked R on the scale; and this condition the 
cobalt retained though left in the last position for some time. 1 found, indeed, that 
small pieces of the iron, nickel, and cobalt, when ignited to remove charge, and then 
held for a moment in any position in the magnetic field, acquired a ciiarge, which 
they retained when out of the field. It would seem, that, even when afterwards 
reversed in the magnetic field, this first charge, or the effect of it, is in part retained, 
but that at high temperatures the metal loses more or less of it; and hence the 
difference between the results at the beginning and end of the series of observations 
marked O. In those marked N the metal was, probably, either in such a condition 
as to have no permanent loss occasioned by heat, or not to have had the heat (of 290° 
only) continued long enou§;h for the purpose. 
3427. I think it very probable that iron and nickel would show like phenomena 
as the cobalt if they were sought for; and also that this quality of charge may affect 
the upsetting angle of pieces of metal differing in their proportions of length and 
thickness (3426.). 
3428. Admitting all the effect of this charge, there is still another result evident 
in both the cobalt series, and in both parts of the series O; that is, the increase of 
power with elevation of temperature. This is, I believe, the first instance in which 
such a result has been recognized ; and even though we might think for a moment 
that, whilst ascending from 66° to 300°, the higher temperatures had set the metal 
more free to give up adverse charge, as above supposed (3426.), still that would not 
account on descending for a diminution of force, without admitting that heat was 
also able to make the metal more favourable to receive charge ; which is in fact to 
say that the power is greater at higher than at lower temperatures. This effect 
cannot depend upon any change in the surrounding medium, for, such is the enormous 
disproportion between it and the cobalt in equal volumes, that if its powers were 
either annihilated or doubled, the effect would be insensible amongst the results. 
If such be the truth with cobalt, then it is probable that a like result would occur 
with iron and nickel at some temperatures, and that in passing to lower temperatures 
than those employed we should arrive at one presenting the maximum magnetic 
induction for each, and below which their inductive force would diminish. Within 
