arts.

PHILIP QUILIBET.

SCIENTIFIC MISCELLANY.

PROTECTION FROM LIGHTNING.

Prof. Clerk Maxwell says that the ordinary lightning rod is a great
mistake. It acts to discharge electricity from the clouds at all
possible opportunities, but these discharges are smaller than would
occur without the rod. The true method is to encase the building in a
network of rods, when it will take its charge quietly like a Leyden jar.
Taking the case of a powder mill, it would be sufficient to surround it
with a conducting material, to sheathe its roof, walls, and ground-floor
with thick sheet copper, and then no electrical effect could occur
within it on account of any thunderstorm outside. There would be no need
of any earth connection. We might even place a layer of asphalte between
the copper floor and the ground, so as to insulate the building. If the
mill were then struck with lightning, it would remain charged for some
time, and a person standing on the ground outside and touching the wall
might receive a shock, but no electrical effect would be perceived
inside, even on the most delicate electrometer.

This sheathing with sheet copper is not necessary. It is quite
sufficient to enclose the building with a network of a good conducting
substance. For instance, if a copper wire, say No. 4, B. W. G. (0.238
inches diameter), were carried round the foundation of the house, up
each of the corners and gables, and along the ridges, this would
probably be a sufficient protection for an ordinary building against any
thunderstorm in this climate. The copper wire may be built into the wall
to prevent theft, but should be connected to any outside metal, such as
lead or zinc on the roof, and to metal rain-water pipes. In the case of
a powder-mill it might be advisable to make the network closer by
carrying one or two additional wires over the roof and down the walls to
the wires at the foundations. If there are water or gas pipes which
enter the building from without, these must be connected with the system
of conducting wires; but if there are no such metallic connections with
distant points, it is not necessary to take any pains to facilitate the
escape of the electricity into the earth. But it is not advisable to put
up a tail pointed conductor.

STEAM MACHINERY AND PRIVATEERING.

Mr. Barnaby, a prominent English naval constructor, has written a
memorandum on the British mercantile marine as an adjun