J 6 Electrical Attractiofi of Quartz. 



property may manifest itself in such a marked manner as 

 to render the readings of the instrument utterly unreliable, 

 and more especially is this the case where the instrument 

 is provided with a quartz cover back and front. In the 

 compass exhibited the back and front of the instrument 

 consist of two plano-convex lenses of quartz with their 

 plane surfaces towards each other, the needle rotating 

 between these covers on an axis, the extremities of which 

 fit into two conical holes in the centre of the quartz covers. 

 In the case of this instrument, the mere act of removing 

 it from the warm pocket is usually sufficient to cause the 

 needle to assume a fixed position in relation to the 

 compass itself and quite unaffected by the magnetic 

 attraction of the earth. If, whilst in this condition, the 

 instrument is rotated, the needle also rotates as if a fixture. 

 If the surface of the quartz be rubbed with the dry finger in 

 a radial direction the needle at once takes up a position in 

 the same direction, and if compelled by shaking to change 

 its position it resumes it when allowed to remain at rest. 

 When the compass is so turned that the axis of the needle 

 is in the direction of the magnetic force of the earth, and 

 the needle therefore in equilibrium, the effects of radial 

 friction become still more marked. As might be expected, 

 the property is not confined to quartz. A compass covered 

 with glass exhibited the same phenomena, with the important 

 difference that in this case the attractive influence ceased 

 with cessation of the friction. That the attractive influence 

 is quite independent of the magnetic force of the needle is 

 proved by the fact that an instrument similar in every 

 respect to the first-mentioned instrument, excepting that 

 the needle was left unmagnetised, exhibited the same 

 phenomena. The action is therefore one of simple eletrical 

 attraction. 



