Mr. E. Gime, whose name is not unknown to our readers, sends us a
description of a certain number of meteorological apparatus to which he has
applied a peculiar method of registering that it is of interest to make
known.
[Illustration: FIG. 1.--DIAGRAM OF GIME'S TELEMAREOGRAPH.]
Mr. Gime in the first place has devised a "telemareograph," that is to say,
an apparatus designed to register at a distance the curve of the motions of
the tide in a given place. The structure of this device, shown
diagramatically in Fig. 1, is very simple. It is divided into two distinct
parts--a transmitter and a registering apparatus. The transmitter consists
of a long glass tube, A, closed at one end and communicating through the
other with a receptacle filled with mercury. A barometric vacuum is formed
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.
The solenoid, S, is interposed in the general circuit, being connected on
the one hand with the line, L, and on the other with a very constant
battery of an electromotive force proportioned to the resistance of the
circuit.
Through the electrode that remains free, the battery is grounded with so
great care that no variation in resistance can be produced thereby. If the
station is near the sea, the conductor of this electrode may be run to a
copper disk, having the same surface as the one at the transmitting
station. With this description, the operation of the apparatus may be
easily understood.
At low water, the pressure of the atmosphere balances a column of mercury
rising in a glass tube to a height proportionate to such pressure. In
measure as the level of the water rises, the pressure on the mercury in the
receptacle increases, and causes the metal to rise in the tube. The higher
the level of the sea, the less becomes the sum of the resistances of the
rheostat, since the column of mercury puts in short circuit all the
divisions of the rheostat, whose contacts are comprised in the height of
the column.
From these variations in the resistance of the circuit naturally result
variations in the current from the battery, B, at the registering station.
To the variations in intensity of the current in the circuit there
correspond variations in the attraction of the solenoid for the core that
transmits these motions to the balance that carries the registering style,
which latter amplifies or reduces them.
The same transmitter suffices for various registering stations arranged in
series, as shown in Fig. 2.
The variations in the resistance of the circuit, due to variations in the
temperature, and the variations in the height of the column of mercury, due
to atmospheric variations, etc., are, according to the inventor, of no
importance.
It would evidently be possible, on the same principle, to construct an
apparatus for registering the indications of a thermometer at a distance.
Such is the principle of Mr. Gime's apparatus. We do not believe that they
are entirely closed to criticism. What, in fact, are the conditions
essential for their proper working? Evidently: (1) the constancy of the
battery used; (2) a rigorously accurate adjustment. This latter condition,
is easily realized; but the same is not the case with the former. Of what
elements shall this constant battery be formed?
Mr. Gime recommends the use of the Latimer-Clark elements. Every one knows
that the Latimer-Clark element is now the best standard of electromotive
force; but let us not forget that this is on condition of its being
employed in open circuit. Now, it is not a question here of an open
circuit, nor even of infinitely weak currents, since in the line we have a
solenoid whose core must set in motion a whole system of connected pieces.
We do not see any possibility of employing Latimer-Clark elements; on the
contrary, it seems to us indispensable to select piles of large discharge,
since the solenoid, S, will attract nothing at all unless a notable
quantity of energy is expended in it.
Is there a pile of this kind so constant as not to render a rigorously
accurate adjustment illusory? Therein lies the entire question, and for our
part we hesitate to pronounce ourselves in the negative.--_La Lumiere
Electrique._
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