tends to place itself parallel to the magnetic axis, the author calls the Magne-crystallic Axis of the crystal. It is perpendicular, or nearly so, to the brightest and most perfect of the four cleavage planes of the crystal. It is the same for all crystals of bismuth. Whether this magne-crystallic axis is parallel or transverse to the magnetic axis, the bismuth is in most cases repelled from a single pole or from the stronger of two poles, its diamagnetic relations being in no way affected. If the crystal be broken up, or if it be fused and resolidified, and the metal then subjected to the action of the magnet, the diamagnetic phenomena remain, but the magnecrystallic results disappear, because of the confused and opposing crystalline condition of the various parts. If an ingot of bismuth be broken up, and fragmentary plates selected which are crystallized uniformly throughout, these also point, the magne-crystallic axis being, as before, perpendicular to the chief plane of cleavage, and the external form, in this respect, of no consequence. The effect takes place when the crystal is surrounded by masses of bismuth, or when it is immersed in water or solution of sulphate of iron, and with as much force apparently as if nothing intervened. The position of the crystal in the magnetic field is affected by the approximation of extra magnets or of soft iron; but the author attributes this result, not to any attractive or repulsive force exerted on the bismuth, but only to the disturbance of the lines of force or resultants of magnetic action, by which they acquire, as it were, new forms. The law of action appears to be that: the line or axis of magnecrystallic force tends to place itself parallel, or as a tangent, to the magnetic curve or line of magnetic force passing through the place where the crystal is situated. Hence the crystal changes its direction with any change in these lines. After noticing the magne-crystallic condition of various bodies, the author enters upon a consideration of the nature of the magne-crystallic force. In the first place, he examines closely whether a crystal of bismuth has exactly the same amount of repulsion, diamagnetic or otherwise, when presenting its magne-crystallic axis parallel or transverse to the lines of magnetic force acting upon it. For this purpose, the crystal was suspended either from a torsion balance or as a pendulum thirty feet in length; but whatever the position of the magne-crystallic axis, the amount of repulsion was the same. In other experiments, a vertical axis was constructed of cocoon silk, and the body to be examined was attached at right angles to it, as a radius. A prismatic crystal of sulphate of iron, for instance, whose length was four times its breadth, was fixed on the axis with its length as radius and its magne-crystallic axis horizontal, and therefore as tangent: then, when this crystal was at rest under the torsion force of the axis, an electro-magnetic pole, with a conical termination, was so placed that the axial line of magnetic force should be, when exerted, oblique to both the length and the magne-crystallic axis of the crystal: and the consequence was, that, when the electric current circulated round the magnet, the crystal actually receded from the magnet under the influence of the force, which tended to place the magne-crystallic and the magnetic axis parallel. Employing a crystal or a plate of bismuth, that body could be made to approach the magnetic pole under the influence of the magne-crystallic force; and this force is so strong as to counteract either the tendency of the magnetic body to approach or of the diamagnetic body to retreat, when it is exerted in the contrary direction. Hence the author concludes that it is neither attraction nor repulsion that causes the set or determines the final position of a magne-crystallic body. He next considers it as a force dependent upon the crystalline condition of the body, and therefore associated with the original malecular forces of the matter. He shows experimentally that as the magnet can move a crystal, so likewise a crystal can move a magnet. Also that heat takes away the power just before the crystal fuses, and that cooling restores it to its original direction. He next considers whether the effects are due to a force altogether original and inherent in the crystal, or whether that which appears in it is not partly induced by the magnetic and electric forces; and concludes that the force manifested in the magnetic field, which appears by external actions and causes the motion of the mass, is chiefly and almost entirely induced, in a manner subject indeed to the crystalline force and additive to it, but at the same time exalting the force and the effects to a degree which they could not have approached without the induction. To this part of the force he applies the word Magneto-crystallic, in contradistinction to magne-crystallic, which is employed to express the condition, or quality, or power which belongs essentially to the crystal. In conclusion, Dr. Faraday remarks "how rapidly the knowledge of molecular forces grows upon us, and how strikingly every investigation tends to develop more and more their importance, and their extreme attraction as an object of study. A few years ago, magnetism was to us an occult power, affecting only a few bodies; now it is found to influence all bodies, and to possess the most intimate relations with electricity, heat, chemical action, light, crystallization, and, through it, with the forces concerned in cohesion; and we may, in the present state of things, well feel urged to continue in our labours, encouraged by the hope of bringing it into a bond of union with gravity itself." (Athenæum, No. 1103, p. 1266.) END OF VOL. I. |