Scientific Intelligence. — Mineralogy. 198 



greenstone, subordinate to clay-slate, in the district of Andreas- 

 berg, in the Hartz. It is worthy of notice, that the same green- 

 stone contains axinite, another species wliich, also like datolite, 

 contains boracic acid. Stromeyer finds its specific gravity to be 

 3.3541 ; and its constituent parts, lime 36.67 ; silica 37.36 ; bo- 

 racic acid 21.26; water 5.71. 



18. Haytorite. — This mineral, which appears to be a variety 

 of rhomboidal quartz, according to Wohler, is composed of sili- 

 ca, 98.5, and iron oxide 0.2. In the analysis a loss of 0.5. 



19. 0)1 the Electricity disengaged by the cleavage of regu- 

 larly crystallized bodies ; by M. Becqnerel. — Many facts shew, 

 that when adhesion takes place between two bodies, in conse- 

 quence of a reciprocal attraction between the surfaces, and one 

 of them is not a good conductor of electricity, they each assume 

 an excess of opposite electricity at the moment of their separa- 

 tion. For example, glass, gum-lac, &c. immersed in mercury, 

 exercise a certain adhesion to it ; and, on being withdrawn, are 

 found to have acquired an excess of electricity, the species of 

 which depends upon particular circumstances, which M. Des- 

 saignes has carefully described. Gum-lac, melted and poured 

 upon glass, contracts an adherence to it, as is known ; on being 

 separated, they each assume an excess of opposite electricity. 

 It is extremely probable that glass, gum-lac, and other bodies 

 immersed in water, would come out electrified, did not the mo- 

 lecules of the liquid stick to their surface, that is to say, did not 

 the affinity of water for these bodies exceed that of the mole* 

 cules for each other. In like manner, in the electrical experi- 

 ments of pressure, there is always obtained a development of 

 electricity, so much the greater the stronger the adhesion be- 

 tween the compressed bodies. For example, on withdrawing 

 from pressure two bits of cork, a slight resistance is sometimes 

 experienced ; the disengagement of electricity is then more con- 

 siderable than if there had been no adhesion. Similar effects 

 are especially observed, when cork or elder pith is pressed against 

 a perfectly polished diamond facet. Some natural philosophers 

 have attributed them to the friction which the molecules expe- 

 rience at the moment of separation of the two bodies. This ex- 

 planation does not appear to be correct, for the above experi- 

 ment evidently proves, that the partial frictions which the mole- 



APRIL — JUNE 1828. N 



