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Miscellanies. . 199 
Bergmeister Schulze, of Duren, in an excursion in the Eifel, a re- 
gion of graywacke and basalt, observed from the top of the Nirburg 
mountain, (a basaltic cone two thousand Prussian feet above the level 
of the Rhine) on an elevation in an eastern direction, something re- 
sembling the ruins of a building. Instead of ruins, however, he found 
it to be two small rocks, about three feet distant from each other in 
their diagonals, about six feet high, with bases not far from three feet 
square: one of them was six feet long and three feet broad; the other 
was a little shorter, but broader. Both rocks were stratified, with a 
dip of twelve hours and parallel to the basaltic range on which they 
teposed. On presenting a magnetic needle to them, it was subject to 
sudden and violent changes. The circumference of one of them at- 
tracted the north pole through half its extent, but repelled it for the re- 
mainder. ‘The manner in which the needle was affected by the other 
tock may be understood by drawing a line lengthwise through the cen- 
ter of the upper plane of the rock, and another crosswise through the 
same plane, so that the point of contact shall occupy the center of the 
Plane: the north pole of the needle was attracted at the extremities 
of the longer line, while the opposite pole was attracted at the extrem- 
ities of the shorter one. 
_M. Reuss, of Berlin, counsellor of mines, observed the same pro- 
Perty in a mountain of dark, grayish, black basalt, free from magnetic 
‘ton stone, in the Mittelgeberg, (lordship of Schréchenstein.) The 
fountain, one thousand eight hundred feet high, is covered with wood 
f0 its summit, and precipitous on all sides. Its polarity is so great, 
that the needle at its eastern foot was moved 40°, and at the summit 
self, 90° W. At the western foot of the rock, the contrary was the 
feet; but the polarity is shown not only in the whole mass of the 
tock, but likewise in the larger detached pieces, and even in the small- 
vst fragments ;—the north point of the needle being at one end distinct- 
Lg attracted, and at the opposite end as distinctly repelled. sl 
These observations, detailed in the Jahrbuch der Chem. u. Phys. of 
Dr. Schweigger, render it possible that the magnetic results obtained 
by Prof, Hitchcock upon the mica-slate mountain of Canaan, in Con- 
heeticut, may be connected with the polarity of rocks; and not de- 
Pendent upon a mass of native iron, as supposed.* 
5. ttrous Atmosphere of Tirhoot.—Tirhoot is one of the principal 
districts in India for the manufacture of saltpetre; the soil is every 
Where abundantly impregnated with this substance, and it floats in the 
"Mosphere in such quantities, that, during the rains and cold weather, 
"sattracted from thence by the lime on the damp walls of houses, and 
uae 
See Vol. xrv, p. 223, of this Journal. 
