ACTION OF HEAT ON M AGNECRYSTALS. 
reasons given (3381.), produce any effect ; neither, for the same reasons, should their 
possible variation by change of temperature produce any effect ; but any change in 
the distance of the magnetic poles would produce an alteration, and I have no doubt 
that, in the first case, the poles were a little nearer to each other, and therefore the 
force at the same temperature greater. It was very satisfactory also to see that the 
two mean lines (selected only by the eye) converged towards each other with rising 
temperatures ; thus at 100° the difference of torsion force is 31, whilst at 200° it is 21 
nearly; as if they were indeed only the tangents of curves, and, at much higher 
temperatures, would coincide or become parallel nearly. 
3402. These first observations are sufficient to show, that the differential magne- 
crystallic force of bismuth diminishes with elevation of temperature, and that to a 
large extent ; that this occurs by a regular progression, which presents no appear- 
ance of any change of sign within the limits of temperature employed ; that the pro- 
gression appears within these limits to be represented by a straight line, or rather by 
a portion of a large curve, a supposition favoured by the approximation of the lines 
at higher temperatures; and that the return of the bismuth to its original degree 
of power is perfect upon the recurrence of the original temperature. 
3403. It is of importance, not merely to examine the effect of temperature upon a 
crystal of bismuth, as one of different raagnecrystals, but to compare the manifesta- 
tion of magnetic force in bismuth when in this state with the corresponding mani- 
festations when the metal is in other conditions, as in the compressed state ; or in the 
amorphous or granular state, at which time it is affected merely as a diamagnetic 
body. I therefore proceeded to compress a piece of granular bismuth in one direc- 
tion, and then cut out of it a short square prism, which, when suspended, was 0‘5 of 
an inch in height and 0'36 in thickness, the line of pressure being horizontal and 
parallel to two of the sides ; when in the magnetic field this line set, of course, equa- 
torially, and the piece therefore, which weighed 128'5 grains, could be subjected to 
experiment in the same manner as the crystal before it (3398.). 
3404. This compressed bismuth acted very well, the difference of torsion force 
being abundantly large enough for observation. The upsetting angle was 109° and not 
very definite, so that currents in the surrounding heated medium (oil) interfered more 
with its exact observance than in the case of the crystal. Such a result was, perhaps, 
to be expected ; for it cannot be supposed that a piece of bismuth, so squeezed in a 
hydraulic press, should have the line of compressing force of equal intensity and like 
direction in all its parts, and therefore comparable, in that respect, to a crystal. The 
results corrected for the upsetting angle were at 
70° F. torsion force was . . 157 
121° F. torsion force was . . 140 
157° F. torsion force was . . 119 
194° F. torsion force \vas . . 116 
211° F. torsion force was . . 106 
and are laid down upon the plate of lines (see bismuth compressed, D). 
