178 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXX.) 
importantly though in an unknown manner ; or else that the bar as a whole exhibits 
some peculiar change connected perhaps with the crossing of the diagram lines 
indicating the ascending and descending results. If the oil of the bath had lost 
diamagnetic power by elevation of temperature (and gain is not to be expected), then 
the carbonate of iron should, on that account alone, have seemed to suffer a loss 
which would be added to its own loss ; such an effect would have tended to give a 
result the reverse of that which in reality appears. 
3424. Experiments were then made, as additions to former results*, upon the metals 
iron, nickel, cobalt, and with much facility, in the following manner. A copper cube 
0-25 of an inch in the side, had a fine hole made through it, in a direction perpen- 
dicular to two of the faces, and a piece of clean soft hon wire 0‘05 of an inch in 
length and 0‘0166 in diameter, was placed in the middle of the hole. The cube, 
which weighed 46 grains, was then suspended as before between the magnetic poles, 
they being 4'86 inches apart. The power of the iron, thus subjected to the magnet, 
was such as to permit the employment of the platinum torsion wire (3369.), and so 
remove every objection as to any possible change of the torsion force. The upsetting 
points were very definite and were 108° apart. The results of the observations, at 
temperatures varying from 30° to 288°, are entered in the chart (see iron bar, P), and 
it will be seen that they present no sensible variation ; as if the inductive force in 
the iron underwent no change during this alteration of temperature, but had obtained 
and kept its maximum degree. We know from other experiments, that at higher 
temperatures the force would decrease; that at a certain temperature the decrease, 
though progressive and not instantaneous (2345.), would be very rapid ; and that at 
still higher temperatures it would again become slow and at last almost insensible: 
and we have reason to suppose that with tourmaline and carbonate of iron we should 
have a like inversion of the curvature if we could descend to very low temperatures. 
3425. Nickel . — A small square bar of pure nickel was prepared; it was 0’09 of an 
inch in length, and 0’036 in thickness. A cube of copper like the former (3424.) had 
a cavity formed in its upper surface, in which the nickel was placed, and retained 
immoveable by the suspending wire, and the whole was submitted to changes of 
temperature. The upsetting angle was 112°. The results are given in the chart 
marked “Nickel bar M,” beginning at the higher temperatures and descending to 
lower. It will be seen that there is a diminution of force at the upper temperature, 
which accords with the general effect of heat ; and as we know that the temperature 
of boiling oil is enough to render even large masses of nickel insensible to the action 
of common magnets, we may believe that a very rapid and interesting series of changes 
would come on between 300° and 600°* 
3426. Cohalt . — A small bar of pure cobalt, 0-08 of an inch in length and 0-027 
square, was in like manner attached to a cube of copper, and subjected to the action 
of the magnet and heat. The upsetting angle was 118°. One reason for the differ- 
* Experimental Researches, 2344-2347 ; also 8vo, vol. iii. p. 444. 
