AND OTMBK CONDITIONS OF MATTEE. 447
another crystal near to, but never actually at, the obtuse angle, as is shown in the sets represented (Fig. 9). This would appear to indicate a turning round of the crystals, so that the line of magnetic force should pass along a line running through and across them, by the obtuse angles in one case, and the acute angles in another. There can be no doubt but that these results point to some general law of arrangement, which may be, by a far more extensive examination of the subject than has yet been made, at length, discovered.
33. We have been in the habit of considering certain metals mag- netic, whilst all the others have been regarded, until the recent researches of Dr. Faraday have shown the contrary to be the case, as without any influence allied to the magnetic. We now know that there is a class opposed to the magnetic class, and which, as it appears, are not merely repelled by magnetic bodies, but have themselves equally strong powers of repulsion. Under this conviction, it at once occurred to me that the crystals of sulphate of iron forming on glass or copper, both diamagnetic bodies, should present something difierent from those form- ing on a plate of iron, or in any magnetic vessel. The result of several experiments proves that crystals of a magnetic body forming on a plate of metal, which belongs to the magnetic class, are less regular, and of a smaller size than those formed on a diamagnetic one ; thus proving, although we have no manifestation of magnetism, as ordinarily shown by its attractive and repulsive power, that a peculiar indication of the existence of powers allied to those under consideration is given by the results obtained by crystallizing salts under diiSerent conditions.
34. Sulphate of copper being allowed to crystallize under similar con- ditions to those observed with the sulphate of iron, it was found, if a strong solution was employed, and, consequently, if the crystallization went on quickly, that they covered the plate pretty uniformly ; but if, by using a weak solution, the force which determines crystalline form was diminished, and the crystallization went on slowly, within the in- fluence of an electro-magnet of considerable power, a very regular order of arrangement was constantly observed. A well-defined circle of crystals appears around the poles, but at some distance from them, within which are perfectly tree spaces. At equal distances from either pole an abundant crop of large crystals form, and there are indications of radiations from this point shown by crystals forming along lines which are curved away from either pole, as if by some mutually repulsive force. These two salts may be considered at present as the representatives of the two classes of crystalline bodies, — ^the magnetic, the protosulphate of iron ; the diamagnetic, the sulphate of copper. In the former, we observe the crystallization marking out the lines of magnetic force ; in the latter, we see an evident tendency to cross those lines, the crystals arranging
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