*574 



SCIENCE. 



Science, e d a portion of a large opaque tourmaline in a steel mor- 

 Curiosities tar ^ fi\\ j t wag re duced to the finest dust. He then placed 

 ir ' the powder upon a plate of glass, from which it slipped 

 S ""Y" 1 *' / 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 the proper temperature, the pow- 

 der 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 at- 

 tractible pcrvder, which adheres to all bodies what- 

 ever. 



This singular breach of analogy between the distri- 

 bution of the pyro-electrical and magnetical forces, 

 has an exact counterpart in the distribution of the 

 doubly refracting forces in regularly crystallized bodies, 

 and in plates of glass that have been rapidly cooled 

 from a red heat. If a crystal of calcareous spar is 

 broken into a thousand fragments, the most minute 

 fragment possesses in miniature the same doubly re- 

 fracting structure as the largest rhomb of that mineral ; 

 whereas the plate of glass that has derived its doubly 

 refracting structure from rapid cooling, comports it- 

 self exactly like a magnetised bar of steel. Any con- 

 siderable portion of the glass, though cut from the po- 

 sitive part, acquires, upon its being detached from the 

 plate, both the positive and the negative structure ; but 

 if it is reduced to very minute fragments, or pounded, 

 these fragments lose their doubly refracting structure; 

 that is, any number of small fragments put together 

 after separation, have not the same doubly refracting 

 force as when they formed part of the plate, the loss 

 of the doubly refracting structure always increasing 

 with the minuteness of the subdivision. 



This striking analogy between the effects of the elec- 

 trical and doubly refracting forces, acquires a new in- 

 terest from the known relations between the forces of 

 electricity and magnetism, and is well worthy of being 

 pursued into all its recesses. 



5. On the Pyro- Electricity of the Poivder of Scolezite and 

 Mesolite, when deprived of their water of' Crystalliza- 

 tion. 



Curiositie 

 in. 



On the py- 

 re-electri- 

 city of the 

 powder of 

 scolezite 

 and me so- 

 lite, when 

 deprived of 

 their water 

 of crystal- 

 lization. 



As the powder of tourmaline, with which the pre- 

 ceding experiments were made, suffered no chemical 

 change by trituration, Dr. Brewster was desirous of 

 trying whether or not the pyro-electricity of minerals 

 existed, when the mineral was deprived of any of its in~ 

 gredients. For this purpose he converted several cry- 

 stals of scolezite and mesolite into a white powder by 

 heat, so as to deprive them of their water of crystal- 

 lization, which is now considered as an essential in- 

 gredient in any mineral species. When the powder 

 was exposed to heat upon a plate of glass, it adhered 

 to it like the powder of tourmaline, and when stirred 

 about by any substance whatever, it collected in masses 



On the pro 

 bable in- 

 fluence of 

 crystallo- 

 graphic 

 compost I io 

 on the dis- 

 tribution o 

 electricity 

 in mineral 



like new fallen snow,* and adhered to the body that Science, 

 was employed to displace it. 



This fact is a very instructive one, and could scarce- 

 ly 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, therefore, developed by the 

 powder, cannot be regarded as a property of the mi- 

 nerals 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-electricity resides, may be easily determined by 

 farther experiments. 



6. On the probable influence of Crystallographic Com- 

 position on the Distribution of Electricity in Minerals. 



Although we have not been fortunate enough to 

 meet with any of those crystals which are necessary in 

 the investigation of this branch of the subject, yet there 

 are some facts of sufficient importance to be noticed in 

 such an inquiry. 



The Abbe Haiiy has particularly mentioned! a cry- 

 stal of topaz, in which the pyro-electricity was distri- 

 buted in a very remarkable manner. He observed 

 that its two extremities were both resinous poles, while 

 the intermediate part gave indications of vitreous elec- 

 tricity. As this phenomenon has been observed only 

 in one mineral, and in one specimen of that mineral, 

 and as it has an exact counterpart in the phenomena 

 of magnetism and of double refraction, it is very pro- 

 bable that the crystal in which it was observed was a 

 compound crystal, in which the two vitreous poles were 

 in contact. 



Although the scolezite and mesolite are both com- 

 posite minerals, yet the faces of composition are paral- 

 lel to the axis of the prism, and therefore cannot affect 

 the distribution of the electricity which is excited by 

 heat. It is therefore in the topaz, and some of the 

 other pyro-electrical minerals, where we must study 

 the influence of composition.! 



7. On the Combats between Electrical Eels and Wild 



Horses. 



In our article on ELECTRICITY, Vol. VIII. p. 477* On the 

 we have already given a very full account of the elec- combats 

 tricity of fishes, and particularly of the Gymnoius dec- between 

 tricus or electrical eel, and of its anatomy, as examined electric eel 

 .by Dr. Hunter. Since that article was printed, how- " 

 .ever^ very curious details have been published by ( 

 Humboldt respecting the electrical eel of South Ame- 

 rica, and the method of catching them by means of 

 wild horses. A brief abstract of the information com- 

 municated by that able traveller will be acceptable to 

 the reader. 



The electrical eels are found both in the large and 

 small rivers of South America, and though they are 

 not easily caught by the Indians from the strength of 

 the current and the depth of the water, yet they often 

 experience electrical shocks from them when they are 

 swimming or bathing. In the environs of Colobozo, 

 however, they occur in great quantities in the basins 



. * The adhesiveness of new fallen snow is doubtless the result of its electrical condition. 



t Traite de Mineralogie, second edition, tome ii. p. 154. We hope that this crystal is in the possession of -the Duke of Buckingham, 

 who, we understand, has cquired the splendid cabinet of the Abbe Haiiy. 



$ Another example of the probable influence of structure on the developement of electricity exists in the Analcime, where the feeble 

 production of electricity by friction, from which Hauy has derived the name of the mineral, is probably owing to its singular mechanical 

 structure. See Edinburgh Transactions, vol. x. p, 187, 193. 



