ecies of
galvanometer as to imitate the motions of the needle. But before it
reached the Red Sea the cable had broken down, and the instrument was
returned dismantled, to be superseded at length by the siphon recorder,
in which the marking point is a fine glass siphon emitting ink, and the
moving body a light coil of wire hung between the poles of a magnet.

The principle of the siphon recorder is exactly the inverse of the
mirror galvanometer. In the latter we have a small magnet suspended in
the centre of a large coil of wire--the wire enclosing the magnet, which
is free to rotate round its own axis. In the former we have a small coil
suspended between the poles of a large magnet--the magnet enclosing the
coil, which is also free to rotate round its own axis. When a current
passes through this coil, so suspended in the highly magnetic space
between the poles of the magnet, the coil itself experiences a
mechanical force, causing it to take up a particular position, which
varies with the nature of the current, and the siphon which is attached
to it faithfully figures its motion on the running paper.

The point of the siphon does not touch the paper, although it is
very close. It would impede the motion of the coil if it did. But the
'capillary attraction' of so fine a tube will not permit the ink to flow
freely of itself, so the inventor, true to his instincts, again called
in the aid of electricity, and electrified the ink. The siphon and
reservoir are together supported by an EBONITE bracket, separate from
the rest of the instrument, and INSULATED from it; that is to say,
electricity cannot escape from them to the instrument. The ink may,
therefore, be electrified to an exalted state, or high POTENTIAL as it
is called, while the body of the instrument, including the paper and
metal writing-tablet, are in connection with the earth, and at low
potential, or none at all, for the potential of the earth is in general
taken as zero.

The ink, for example, is like a highly-charged thunder-cloud supported
over the earth's surface. Now the tendency of a charged body is to move
from a place of higher to a place of lower potential, and consequently
the ink tends to flow downwards to the writing-tablet. The only avenue
of escape for it is by the fine glass siphon, and through this it rushes
accordingly and discharges itself in a rain upon the paper. The natural
repulsion between its like electrified particles causes the shower