CHANGE OF THE ABSOLUTE MAGNETIC FORCE BY HEAT. 
177 
with before, is included in such investigations, by the dependence in a greater or 
smaller degree of the motions of the body upon the medium around it ; for if the 
latter were to change by differences of temperature, the former would seem to have 
suffered a change though none might have occurred. The statement made on a 
former occasion (2359.), that paramagnetic solutions were not affected by heat, can 
hardly be accepted, without further confirmation, in the present state of the subject. 
If bodies at magnetic zero suffer no alteration by heat, then a fluid having that con- 
dition might be selected as a bath in which to try the changes of solid bodies not at 
zero ; and a solid at zero might in like manner be employed to ascertain the varia- 
tions by heat in the fluids surrounding it* : further, if paramagnetic solutions suffer 
no change, they may be employed to exalt the indications of diamagnetic bodies, such 
as bismuth or phosphorus. In the mean time the following results may be useful and 
acceptable. 
3422. Being very desirous of knowing whether the variation of a piece of amor- 
phous, i. e. granular, bismuth had the same progression for the same temperatures as 
a crystal of bismuth, I endeavoured to obtain some measures, but did not satisfy 
myself. I employed a bar of the metal about 0’55 of an inch long and 0T2 of an 
inch thick, between pointed poles; but the force of the bismuth under the influence 
of the Logeman magnet was not sensible with a metallic torsion wire, and when a 
silk suspender was used (uncertain in itself), the indications were altogether over- 
come by currents in the surrounding fluid. A tourmaline crystal was just as un- 
favourable under the like circumstances ; besides which, it must be understood that 
as tourmalines differ much from each other, specimens from the same crystal can 
only properly be compared, 
3423. * Carbonate of iron. — I found this substance sufficiently paramagnetic to 
supply indications with the Logeman magnet, when the pointed poles were employed 
and placed r95 inch apart. The crystal formerly described (3379.) was therefore 
reduced by grinding to a plate, which being suspended with the optic axis or short 
diameter vertical, was then 0'6 of an inch in length, 0T7 in breadth, and 0‘37 in 
height ; a small copper cube was hung to it beneath, so as to give it weight in the 
oil-bath, and prevent its approach as a whole to either one or the other pole. The 
results obtained are entered in the diagram of curves (see carbonate of iron bar, E). 
They are not accordant with those given by the same substance as a magnecrystal. 
In the ascending part of the series the force at 126° is 157, and at 288° it is 133 ; the 
diminution 24 being only of the force at 126°. In the descending part, the force 
at 96° is 182, and at 292° it is 125, the difference 57 being of the force at 96°: 
both differences are much less than that with the crystal of carbonate of iron, for 
then the force at 96° was 255, and at 292° was 137, the difference 118 being almost 
half of the force at 96°. It is evident therefore that the forces of the bar do not 
diminish in the same ratio as the forces of the crystal ; or else that the medium alters 
* Royal Institution Proceedings, Jan. 1853, p. 232 ; or Experimental Researches, 8vo. vol. iii. p. 500. 
