ATTRACTION AND REPULSION OF THE SAME MAGNETIC SUBSTANCE. 167 
was then able to approach the pole until separated only by the thickness of the glass 
of the vessel. 
3390. A saturated solution of protosulphate of iron was prepared at a temperature 
of 65° Fahr., and a little sulphuric acid added to prevent the occurrence of turbidness 
upon the addition of water. This solution, more or less diluted, was put into the 
glass vessel, and when its motion had ceased, the crystal was placed on the balance 
and adjusted near the pole; then the magnet was excited by a voltaic battery and 
the elfect observed. When the axis of the prism was in the magnetic axis, the crystal 
was repelled in all solutions stronger than one consisting of about eleven volumes of 
the saturated solution and six of water; in weaker solutions it was attracted, the 
force of attraction and repulsion varying, of course, as the medium varied. When 
the crystal axis was equatorial, i. e. when the chief magnecrystallic axis coincided 
with the magnetic axis of the field, then the crystal was repelled in all solutions 
stronger than one consisting of about eighteen volumes of the saturated solution and 
six of water. Hence there is a range of medium, varying in strength from that 
produced by adding either two or three volumes of the saturated solution to one 
volume of water, within which the crystal in one position is attracted and in the 
other repelled ; and, as might be expected, a mixture of fourteen or fifteen volumes 
of solution with six of water, forms a medium in which the attraction and repulsion 
were nearly equal to each other. It was very easy in any of these media, to find 
a position for the crystal (by turning it on the vertical axis) in which it was neither 
attracted nor repelled. A second and a third crystal were, in succession, put upon 
the balance and gave exactly the satne results. 
3391. The red ferroprussiate of potassa is a crystal so paramagnetic as to be 
attracted in all positions in space. I therefore turned to calcareous spar, which, 
though it be diamagnetic in air, is not necessarily so in space, since air is, because of 
its oxygen, a magnetic body (2791.). Possessing a sphere of calcareous spar, given 
to me by Professor W. Thomson, I tried it first in water, and found, that whether the 
optic axis was placed equatorial or axial in relation to the magnetic field, the sphere 
was attracted, though more in the former case than in the latter. Hence the body is 
less diamagnetic than water and so approaches to a vacuum. In order to compare 
it with a vacuum I employed carbonic acid as the medium *, but then found that in 
both positions it was repelled ; hence its differential range as a magnecrystal cannot 
include the magnetic force exerted in space merely. 
3392. This sphere is repelled in all positions in alcohol ; therefore it would be easy, 
by the addition either of alcohol or a little solution of iron to water, to obtain a 
liquid intermediate in force between the forces of the sphere in its two positions. 
3393. But though pure calcareous spar will not include space, yet it is probable 
that some crystals may be found by trial which will do so. I have various specimens 
of calcareous spar, which contain in combination minute portions of iron, and being 
* Royal Institution Proceedings, Jan. 21, 1853, p. 233 ; or Experimental Researches, Svo, vol. hi. p. 502. 
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