198 Jlliscellanies, 



3. Neil) analysis of Brewsterite. — Mr. Connell has repeated the 

 analysis of this mineral, which Retzius, according to Berzelius, found 

 to contain Silica, - - 57.285 



Alumina, - - 17.011 



Lime, J - ■ ^-^64 



Water, - - - 17.872 



99.932 



Mr. Connell's specimens were from Strontian, and gave 

 Silica, - - 53.666 



Alumina, - > - 17.492 



Strontia, - - 8.325 ) -. - p.«, . 



Baryta, - - - 6.749 \ ^^•"''* 



Lime, - - 1.346 



Oxide of iron, - - .292 



Water, - - 12.584 



100.454 



Sr 

 Its formula may be expressed by —- S^ +4AS3-{-6Ag ; or, if we 



suppose the proportion of the strontia and baryta to be 2 atoms of the 

 former to 1 of the latter, the constitution will then be, 2 atoms bisili- 

 cate of strontia +1 atom bisilicate of baryta -f 12 atoms tersilicate of 

 alumina _j-6 atoms of water. — {Idem. Jan. 1831, p. 35.) 



4. Polarizing Rocks. — The first observations concerning the mag- 

 netic polarity of rocks were made by Baron Humboldt in 1796. He 

 noticed it in a serpentine rock on the Haidberg, near Celle, in the coun- 

 try of Baireuth. It was afterwards observed in many other rocks, such 

 as hornblende-slate, porphyry, trachyte, basalt, &c.* It is appar- 

 ently confined to mountains containing magnetic iron-stone, although 

 the quantity of this admixture in itself does not limit the intensity of 

 the property ; as indeed it shows itself with different purely magnetic 

 iron stones in the greatest variety of degrees of strength, and there 

 are some of these which show no magneto-polar action. Neither is 

 there any regularity in the position of the axes either in one and the 

 same mass of rock in general, or a fixed correspondence, in the posi- 

 tion of these axes, with the direction of the strata of the rocks. 



* For the discovery of Humboldt and those connected with it, see the Intelligenz 

 Blatt Algemeine Literaturzeitung, 1796 and 1797. JVeues Bergmann's Jour, i, 

 pp. 257 and 542. Gren's JSTeues Jour. d. Chem. u. Phys. iv. V. Moll's Jahr. d. 

 Berg. u. Hutten Kunde, m, p. 301. V. Moll's JVeues Jahr. d. B. u. H. ii, p, 403. 

 Gilbert's JLnnalen, neue Folge, xiv. Heft i, p. 89. Goldfusz and Bischol's Phisik. 

 Statist. Bcschreiburg d. Fichtelgeberges, i, p. 139, and ibid, altere Reihe, xviii, p. 

 297. 



