Royal Society. 77 



lance, or as a pendulum thirty fevjt in length ; but whatever the 

 position of the magnecrystallic 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 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 magnecrystallic axis horizontal, and there- 

 fore as tangent ; then, when this crystal was at rest under the torsion 

 force of the silken axis, an electro-magnetic pole was so placed, 

 that the axial line of magnetic force should be, when exerted, ob- 

 lique to both the length and the magnecrystallic 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 axis and the magnetic axis parallel. Employing a crystal 

 or plate of bismuth, that body could be made to approach the mag- 

 netic pole under the influence of the magnecrystallic 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 which causes the set or deter- 

 mines the final position of a magnecrystallic body. 



He next considers it as a force dependent upon the crystalline con- 

 dition of the body, and therefore associated with the original mole- 

 cular forces of the matter. He shows experimentally, that, as the 

 magnet can move a crystal, so also a crystal can move a magnet. 

 Also, that heat takes away this power just before the crystal fuses, 

 and that cooling restores it in its original direction. He next con- 

 siders 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 he 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 crystalhne 

 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 mag- 

 neto-cry stallic, in contradistinction to the word magnecrystallic, 

 which is employed to express the condition, or quality, or power, 

 which belongs essentially to the crystal. 



The author then remarks upon the extraordinary character of the 

 power, which he cannot refer to polarity ; and gives expression to 

 certain considerations and views which will be best learned from the 

 paper itself. After this, he resumes the consideration of Pliicker's 

 results "upon the repulsion of the optic axes of crystals" already re- 

 ferred to, and arrives at the conclusion that his results and those 

 now described have one common origin and cause. He then con- 

 siders Pliicker's results in relation to those which he formerly ob- 

 tained with heavy optical glass and many other bodies. In con- 



