SUPPOSED POLARITY OF DIAMAGNETIC BODIES. 
175 
such as to cause five or six approaches and withdrawals of the core in one second ; 
yet the solution produced no sensible indication at the galvanometer. A piece of 
magnetic glass tube (2354.), and a core of foolscap paper, magnetic between the 
poles of the electro-magnet, were equally ineffieient. A tube filled with small crystals 
of protosulphate of iron caused the needle to move about 2°, and cores formed out of 
single large crystals, or symmetric groups of crystals of sulphate of iron, produced the 
same effect. Red oxide of iron (colcothar) produced the least possible effect. Iron 
scales and metallic iron (the latter as a thin wire) produced large effects. 
2654. Whenever the needle mov^ed, it was consistent in its direction with the effect 
of a magnetic body ; but in many cases, with known magnetic bodies, the motion 
was little or none. This proves that such an arrangement is by no means so good a 
test of magnetic polarity as the use of a simple or an astatic needle. This deficiency 
of pow’er in that respect does not interfere with its ability to search into the nature 
of the phenomena that appear in the experiments of Weber, Reich and others. 
2655. Other metals than iron were now employed and with perfect success. If 
they were magnetic, as nickel and cobalt, the deflection was in the same direction as 
for iron. When the metals were diamagnetic, the deflection was in the contrary direc- 
tion ; and for some of the metals, as copper, silver and gold, it amounted to 60° or 70°, 
which was permanently sustained as long as the machine continued to work. But 
the deflection was not the greatest for the most diamagnetic substances, as bismuth 
or antimony, or phosphorus ; on the contrary, I have not been able to assure myself, 
up to this time, that these three bodies can produce any effect. Thus far the effect 
has been proportionate to the conducting power of the substance for electricity. Gold, 
silver and copper have produced large deflections, lead and tin less. Platina very little. 
Bismuth and antimony none. 
2656. Hence there was every reason to believe that the effects were produced by 
the currents induced in the mass of the moving metals, and not by any polarity of 
their particles. I proceeded therefore to test this idea by different conditions of the 
cores and the apparatus. 
2657. In the first place, if produced by induced currents, the great proportion of 
these would exist in the part of the core near to the dominant magnet, and but little 
in the more distant parts ; whereas in a substance like iron, the polarity which the 
whole assumes makes length a more important element. I therefore shortened the 
core of copper from 5^ inches (2643.) to 2 inches, and found the effect not sensibly 
diminished ; even when 1 inch long it was little less than before. On the contrary, 
when a fine iron wire, 5| inches in length, was used as core, its effects were strong; 
when the length was reduced to 2 inches, they were greatly diminished ; and again, 
with a length of 1 inch, still further greatly reduced. It is not difficult to construct 
a core of copper, with a fine iron wire in its axis, so that when above a certain 
length it should produce the effects of iron, and beneath that length the effects 
of copper. 
