This instrument consists of a glass tube, sealed at one end, and
furnished with a brass cap at the other end, through which the air
is admitted by a very small aperture. Nearly fill the tube with the
following solution: camphor, 2½ drams; nitrate of potash, 38 grains;
muriate of ammonia, 38 grains; water, 9 drams; rectified spirit,
9 drams. Dissolve with heat. At the ordinary temperature of the
atmosphere, plumose crystals are formed. On the approach of stormy
weather, these crystals appear compressed into a compact mass at the
bottom of the tube; while during fine weather they assume their plumose
character, and extend a considerable way up the glass. These results
depend upon the condition of the air, but they are not considered to
afford any reliable indication of approaching weather.