in this tube. The level of the open receptacle corresponds exactly to the
level of the lowest tide.

[Illustration: FIG. 2.--THE APPARATUS WITH THREE REGISTERING STATIONS.]

Pieces of iron wire projecting sufficiently in the interior to establish
good contacts with the column of mercury are fastened one millimeter apart
to the inner surface of the tube. These iron contacts are connected with
the divisions of a rheostat, R, arranged in a tight compartment surrounded
with paraffine, near the tube.

This rheostat is interposed in the general circuit. It is connected through
one extremity with the line, and through the other with a disk of copper,
which has a surface of one square meter, and is immersed in the sea.

The line, L, insulated like an ordinary telegraph wire, is prolonged as far
as to the registering station.

The registering apparatus consists of a solenoid, S, that acts upon a soft
iron core suspended by a cord from the extremity, _x_, of the beam of a
balance. This cord passes between the channels of two rollers designed,
despite the motion of the beam, to keep the core in a vertical position in
the center of the solenoid.

The opposite arm of the balance carries a sliding weight, _i_, that moves
over a graduated scale and is designed to balance the core, N, in a certain
position in regulating the motions of the curve. At its extremity it
carries a style that bears against the drum, T, on which the paper is wound
that is to receive the mareometric curve.