154 Scientific Notices — Magnetism. [Feb. 



contiguous to the base, sometimes of the size of three or four 

 hues in every direction. They are generally engaged in blende, 

 which is cleavabie in large laminse, and are composed in the 

 interior of a delicate tissue of minute crystals, between which 

 numerous cavities are conspicuous, lined with these crystals. 

 Sometimes also the large pseudomorphous crystals are quite 

 disengaged, and accompanied by arsenical pyrites, chlorite, 

 quartz, &c. The colour of the streak is almost of the same 

 colour in the pseudomorphous crystals, and the blende in which 

 they are imbedded. — (Edinburgh Journal of Science.) 



10. English Locali/.i/ of Metallic Lead. 



This substance has lately been found in situ in the neigh- 

 bourhood of Alston. It uccurs in small globular masses, imbed- 

 ded in galena and a slaggy substance, accompanied with red 

 litharge, crystals of blende and quartz. The vein in which it is 

 found is in limestone, and of the thickness of an inch, widening 

 out to two or three as it goes down. The whole mass within 

 the vein is considerably decomposed, and the ore is found in 

 incoherent pieces, some of which are about the size of a walnut. 

 Many of them have a very slaggy appearance, both externally 

 and internahy, while others are pure galena, distinctly cleava- 

 bie, and coated with a white mealy sulphate of lead, produced 

 by decomposition. A more particular notice of this mineral 

 will probably soon be given. — (Edin. Jour, of Science.) 



Magnbtism. 



11. Gai/'Lnssac on the mutual Action of two Magnetic Particles 



in different Bodies. 



This very interesting experiment was undertaken by M. Gay- 

 Lussac at the request of M. Poisson, for the purpose of ascer- 

 taining whether or not the mutual action of two magnetic parti- 

 cles depended on the matter of each of the bodies, whicn was 

 found to be the case. 



A magnetical needle, eight inches long, was found to make 

 ten horizontal vibrations near the direction of the magnetic 

 meridian in 131 seconds. A prismatic bar of soft iron, about 

 eight inches long, three-fourths of an inch wide, and one- 

 eighteenth of an inch thick, in a vertical direction, was now fixed at 

 the distance of two inches below the needle, and in the plane of 

 the magnetic meridian. The oscillations of the needle became 

 more frequent, being about 10 in 65 seconds, and soon after 10 

 in 60 seconds. 



A similar and equal bar of pure nickel was now substituted in 

 place of the iron bar, and the needle made at first 10 oscilla- 

 tions in 78 seconds, and soon after 10 in 77 seconds. When 

 the bar of nickel was removed, the needle made 10 oscillations 

 in 130 seconds by the action of the earth alone. M. Foisson's 

 Memoir on Magnetism. — (Edin. Jour, of Science.) 



