DIRECTION OF INDUCTIVE POLARITY — IN CRYSTALS. 269 



with nitrogen, when the small negative or the large positive ball was rendered in- 

 ductric, the effects corresponded with those which in oxygen were produced when 

 the small positive or the large negative was rendered inductric. 



1688. In such solid bodies as glass, lac, sulphur, &c., the particles appear to be able 

 to polarize in all directions, for a mass when experimented upon so as to ascertain 

 its inductive capacity in three or more directions (1690.), gives no indication of a dif- 

 ference. Now as the particles are fixed in the mass, and as the direction of the in- 

 duction through them must change with its change relative to the mass, the constant 

 effect indicates that they can polarize electrically in any direction. This accords 

 with the view already taken of each particle as a whole being a conductor (1669.), 

 and, as an experimental fact, helps to confirm that view. 



1689. But though particles may thus polarize in any direction under the influence 

 of powers which are probably of extreme energy (1686.), it does not follow that each 

 particle may not tend to polarize to a greater degree, or with more facility, in one 

 direction than another ; or that different kinds may not have specific differences in 

 this respect, as they have differences of conducting and other powers (1296. 1326. 

 1395.). I sought with great anxiety for a relation of this nature; and selecting cry- 

 stalline bodies as those in which all the particles are symmetrically placed, and there- 

 fore best fitted to indicate any result which might depend upon variation of the di- 

 rection of the forces to the direction of the particles in which they were developed, 

 experimented very carefully with them. I was the more strongly stimulated to this 

 inquiry by the beautiful electrical condition of those crystalline bodies tourmaline and 

 boracite, and hoped also to discover a relation between electric polarity and that of 

 crystallization, or even of cohesion itself (1316.). My experiments have not esta- 

 blished any connexion of the kind sought for. But as I think it of equal importance 

 to show either that there is or is not such a relation, I shall briefly describe the re- 

 sults. 



1690. The form of experiment was as follows. A brass ball 0*73 of an inch in 

 diameter, fixed at the end of a horizontal brass rod, and that at the end of a brass 

 cylinder, was by means of the latter connected with a large Leyden battery (291.) 

 by perfect metallic communications, the object being to keep that ball, by its con- 

 nexion with the charged battery in an electrified state, very nearly uniform, for half 

 an hour at a time. This was the inductric ball. The inducteous ball was the carrier 

 of the torsion electrometer (1229. 1314.); and the dielectric between them was a cube 

 cut from a crystal, so that two of its faces should be parallel to the optical axis, whilst 

 the other four were perpendicular to it. A small projecting piece of shell-lac was 

 fixed on the inductric ball at that part opposite to the attachment of the brass rod, 

 for the purpose of preventing actual contact between the ball and the crystal cube. 

 A coat of shell-lac was also attached to that side of the carrier ball which was to be 

 towards the cube, being also that side which was furthest from the repelled ball in the 

 electrometer when placed in its position in that instrument. The cube was covered 



