become electrified in contrary
senses. If the bird flies toward the ground, flapping its wings, it
compresses the air below them, and, supposing that the wing feathers
can bend aside, the experiments of Exner show that by the friction the
upper side of one feather and the lower side of that which is just
above are electrified oppositely, the more powerfully as the rubbing
is greater, which always causes them to resume the normal
position.--L'Electricien.

* * * * *

SELECTED FORMULAE.

REMOVAL OF INK FROM HECTOGRAPH.--It is recommended in Suedd. Ap. Ztg.
to pour crude hydrochloric acid upon the hectograph, rub with a wad of
cotton, then wash off by holding under cold running water and drying
with a cloth. The hectograph may be used again immediately.

TO CLEAN WALL PAPER.--Four ounces of pumice stone in fine powder are
thoroughly mixed with 1 quart of flour and the mass is kneaded with
water enough to form a thick dough. This dough is formed into rolls
about 2 inches in diameter and 6 or 8 inches long; each one is sewed
up in a piece of cotton cloth and then boiled in water for from 40 to
50 minutes--long enough to render the dough firm. After cooling and
allowing the rolls to stand for several hours, the outer portion is
peeled off and they are then ready for use, the paper being rubbed
with them as in the bread process.--Druggist's Circular.

INSULATING COMPOUND.--Prof. Fessenden recommends for armature work a
compound made by boiling pure linseed oil at about 200 degrees with
1/2 per cent. of borate of manganese, the boiling being continued for
several hours, or until the oil begins to thicken. An advantage of
this borated oil is that it always retains a slight stickiness, and so
gives a good joint when wrapped around wires, etc. Many substances so
used are not sticky and let moisture in through the joints. Where a
smooth surface is required, it is readily obtained by dusting on a
little talc. It can also be given a coat of japan on the
outside.--American Electrician.

HOW TO CLEAN DIATOMS.--As a general rule, we may say that every
specimen of diatomaceous earth or rock needs a special treatment. The
following, however, may serve as a basic treatment, from which such
departure may be taken in each case as the nature of the specimen
would indicate: Boil the material in hydrochloric acid, in a test
tube, from two to five minutes. Let settle, pour off the hydrochloric
acid,