If you can
count from two to three seconds between the appearance of the lightning
and the sound, there is seldom much danger; and when the interval is a
quarter of a minute, you are secure.--_Brande's Lectures.--Lancet._
_New Crane._
A crane for raising weights, on an entirely new principle--that of the
application of the lever, assisted by wedges, instead of the usual
plan of wheel and pinion, for multiplying power--has recently been
constructed at the West India Docks. The power of two men, with the
patent crane, is stated to be capable of lifting from 2-1/2 to 3 times
the weight lifted through the same space in a given time, by the best
constructed cranes on the old principle of wheel machinery.
_Etching on Ivory_.
The usual mode of ornamenting ivory in black, is to engrave the pattern
or design, and to fill up the cavities thus produced with hard black
varnish. Mr. Cathery has much improved and simplified the process, by
covering the ivory with engraver's varnish, and drawing the design with
an etching needle; he then pours on a menstruum, composed of 120 grains
of fine silver, dissolved in an ounce measure of nitric acid, and
diluted with one quart of pure distilled water. After half an hour, more
or less, according to the required depth of tint, the liquor is to be
poured off, and the surface is to be washed with distilled water, and
dried with blotting paper. It is then to be exposed to the light for
an hour, after, which the varnish may be removed by oil of turpentine.
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