The accompanying cut illustrates a telemeter which was exhibited at the
Paris Exhibition of Electricity, and which is particularly interesting
from the fact that it is the first apparatus of this kind. It will be
remembered that the object of a telemeter is to make known at any moment
whatever the distance of a movable object, and that, too, by a direct
reading and without any calculation. In Mr. Siemens' apparatus the
problem is solved in the following manner:
The movable object (very often a vessel) is sighted from two different
stations--two points of the coast, for example--by two different
observers. The sighting is done with two telescopes, A1 and A2, which
the observers revolve around a vertical axis by means of two winches, K1
and K2, that gear with two trains of clockwork. There is thus constantly
formed a large triangle, having for its apices the movable point sighted
and the vertical axes, A1 and A2, of the two telescopes. On another
hand, at a point situated between the two telescopes, there is a table,
T T, that carries two alidades, a1v1, and a2v2, movable around their
vertical axes, a1 and a2. The line, a1 a2, that joins these axes is
parallel with that which joins the axes of the two telescopes; and the
alidades are connected electrically with the telescopes by a system
such that each alidade always moves parallel with the telescope that
corresponds to it. It follows from this that the small triangle that
has for apices, a1 a2, and the crossing point of the two alidades will
always be like the large triangle formed by the line that joins the
telescopes and the two lines of vision. If, then, we know the ratio of
a1, a2 to A1 A2, it will suffice to measure on one of the alidades the
distance from its axis to the point of crossing in order to know the
distance from the movable object to the axis of the corresponding
telescope. If the table, T T, be covered with a chart giving the space
over which the ship is moving, so that a1 and a2 shall coincide with the
points which A1 and A2 represent, the crossing of the threads of the
alidades will permit of following on the chart all the ship's movements.
In this way there maybe had a powerful auxiliary in coast defence; for
all the points at which torpedoes have been sunk may be marked on the
chart, and, as soon as the operator at the table finds, by the motion
of the alidades, that the ship under observation is directly over a
torpedo, he will be able to fire the latter and blow the enemy up.
During this time the two observers at A1 and A2 have only to keep their
telescopes directed upon the vessel that it has been agreed upon to
watch.
[Illustration: SIEMENS' ELECTRIC TELEMETER]
In order to obtain a parallelism between the motion of the alidades and
that of the corresponding telescopes, the winch of each of the latter,
while putting its instrument in motion, also sets in motion a Siemens
double-T armature electromagnetic machine. One of the wires of the
armature of this machine, connected to the frame, is always in
communication with the ground at E1 (if we consider, for example, the
telescope to the left), and the other ends in a spring that alternately
touches two contacts. One of these contacts communicates with the
wire, L1 and the other with the wire, L3, so that, when the machine is
revolving, the currents are sent alternately into L1 and L3. These two
latter wires end in a system of electro magnets, M1, provided with a
polarized armature. The motions of the latter act, through an anchor
escapement, upon a system of wheels. An axle, set in motion by the
latter, revolves one way or the other, according to the direction of the
telescope's motions. This axle is provided with an endless screw that
gears with a toothed sector, and the latter controls the rotatory axis
of the alidade. The elements of the toothed wheels and the number of
revolutions of the armature for a given displacement of the telescope
being properly calculated, it will be seen that the alidade will be able
to follow all the movements of the latter.
When it is desired to place one of the telescopes in a given position
(its position of zero, for example), without acting on the alidade,
it may be done by acting directly on the telescope itself without the
intermedium of the winch. For such purpose it is necessary to interrupt
communication with the mechanism by pressing on the button, q. If the
telescope be turned to one side or the other of its normal position,
in making it describe an angle of 90°, it will abut against stops, and
these two positions will permit of determining the direction of the
base.
The alidades themselves are provided with a button which disengages the
toothed sector from the endless screw, and permits of their being
turned to a mark made on the table. A regulating screw permits of this
operation being performed very accurately. In what precedes, we have
supposed a case in which the movable point is viewed by two observers,
and in which the table, T T, is stationed at a place distant from them.
In certain cases only two stations are employed. One of the telescopes
is then placed over its alidade and moves with it; and the apparatus
thus comprehends only a system of synchronous movements.
This telemeter was one of the first that was tried in our military
ports, and gave therein most satisfactory results. The maneuver of the
winch, however, requires a certain amount of stress, and in order that
the sending of the currents shall be regular, the operator must turn it
very uniformly. This is a slight difficulty that has led to the use
of piles, instead of the magneto-electric machine, in the apparatus
employed in France. With such substitution there is need of nothing more
than a movable contact that requires no exertion, and that may be guided
by the telescope itself.--_La Lumière Electrique_.
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