1824.] Scientijic Notices — Mineralogy. 471 



more remarkable than that which is exhibited, by cutting a piece 

 from one of their extremities. If the piece is taken from the 

 north pole of the magnet, it is itself a regular magnet, with 

 north and south polarity. The very same property was disco- 

 vered in the tourmaline by Mr. Canton, who found that if it was 

 broken into two parts, when in a state of excitation by heat, 

 each fragment had two opposite poles. 



" If we attempt, however, to reduce the magnet into minute 

 portions by any mechanical operation, such as filing, pounding, 

 &c. the particles of steel are found to be deprived of their mag- 

 netical qualities, their coercive power being destroyed by the 

 vibrations or concussions which are inseparable from the process 

 of comminution ; and analogy would lead us to expect the same 

 result with the tourmaline. 



" In order to ascertain this point, I pounded a portion of a 

 large opaque tourmaline in a steel mortar, till it was reduced to 

 the finest dust. I then placed the powder upon a plate of glass, 

 from which it slipped off, by inclining the glass, like all other 

 hard powders, without exhibiting any symptoms of cohesion 

 either with the glass, or with its own particles. When the glass 

 was heated to its proper temperature, the powder stuck to the 

 glass ; and when stirred with any dry substance, it collected in 

 masses, and adhered powerfully to the substance with which it 

 was stirred. This viscidity, as it were, or disposition to form 

 clotted masses, diminished with the heat, and at the ordinary 

 temperature of the atmosphere, it recovered its usual want of 

 coherence. 



" Hence it follows, that the tourmaline preserves its pyro- 

 electricity even in the state of the finest dust, and that this dust, 

 when heated, is an universally attractible powder, which adheres 

 to all bodies whatever." 



Powdered scolezite and mesolite, after being deprived of 

 their water of crystallization, exhibited similar pyro-electrical 

 effects with powdered tourmaline. 



" This fact," says Dr. Brewster, " is a very instructive one, 

 and could scarcely have been anticipated. As several minerals 

 differ only in the quantity of their water of crystallization, the 

 powder which was thus pyro-electrical, could not be considered 

 either as scolezite or mesolite, but as another substance not 

 recognised in mineralogy. The pyro-electrical property, there- 

 fore, developed by the powder, cannot be regarded as a property 

 of the minerals of which the powder formed a part, but merely 

 as a property of some of their ingredients. In which of the 

 ingredients, or in what combination of them, the pyro-electri- 

 city resides, may be easily determined by farther experiments." 

 — (Edinburgh Journal of Science.) 



