Magneto-optic Properties of Crystals, 1 3 



to present to us a new force, or a new form of force in the 

 molecules of matter, which for convenience sake, I will con- 

 ventionally designate by a new word, as the magnecrystallic 

 force*." 



"The magnecrystallic force appears to be very clearly 

 distinguished from either the magnetic or diamagnetic forces, 

 in that it causes neither approach nor recession ; consisting 

 not in attraction or repulsion, but in its giving a certain de- 

 terminate position to the mass under its influence, so that a 

 given line in relation to the mass is brought by it into a given 

 relation with the direction of the external magnetic powerf." 



The line through the crystal which sets itself with greatest 

 force from pole to pole, is termed by Mr. Faraday the magne- 

 crystallic axis of the crystal. He proves by experiment that 

 bismuth has exactly the same amount of repulsion whether 

 this axis be parallel or transverse to the lines of magnetic force 

 acting on it. 



" In other experiments a vertical axis was constructed of 

 cocoon silk, and the body to be examined was attached to it 

 at right angles 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 magne- 

 crystallic axis horizontal, and therefore 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, oblique to 

 both the length and the magnecrystallic axis of the crystal ; 

 and the consequence was, that, when the electric current cir- 

 culated round the magnet, the crystal actually receded from 

 the magnet under the influence of the force, which tended to 

 place the magnecrystallic axis and the magnetic axis parallel. 

 Employing a crystal or plate of bismuth, that body could be 

 made to approach the magnetic 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 ap- 

 proach or of the diamagnetic body to retreat, when it is ex- 

 erted in the contrary direction. Hence Mr. Faraday con- 

 cludes that it is neither attraction nor repulsion which causes 

 the set or determines the final position of a magnecrystallic 

 body J." 



" As made manifest by the phenomena, the magnecrystallic 

 force is a force acting at a distance, for the crystal is moved 

 by the magnet at a distance, and the crystal can also move 

 the magnet at a distance." Mr. Faraday obtained the latter 

 result by converting a steel bodkin into a magnet, and suspend- 



* Phil. Trans., 1849, p. 4. f Phil. Trans., 1849, p. 22. 



X Phil. Mag. vol, xxxiv. p, 77. 



