An examination of the friction in screws having their threads of various
forms, has led M. Poncelet to this very important conclusion, namely,
that the friction in screws with square threads is to that of equal
screws with triangular threads, as 2.90 to 4.78, proving a very
important advantage of the former over the latter, relative to the loss
of power incurred in both by friction.--_Brande's Journal._


_Fulminating Powder._

According to M. Landgerbe, a mixture of two parts nitre, two parts
neutral carbonate of potash, one part of sulphur, and six parts of
common salt, all finely pulverized, makes a very powerful fulminating
powder. M. Landgerbe adopts the extraordinary error of supposing that
these preparations act with more force downwards than in any other
direction.--_Bull. Univ._


_Aurora Borealis._

An aurora borealis was seen from North End, Hampstead, near London, from
about seven o'clock until eleven, on the evening of Dec. 1. It generally
appeared as a light resembling twilight, but shifting about both to the
east and the west of north, and occasionally forming streams which
continued for several minutes, and extended from 30 to 40 degrees high.
The light on the horizon was not more than 12 or 15 degrees in
height.--_Brande's Journal._