Next suppose them, still remaining parallel, in the positions C1 and D1.
The total resistance of the circuit is now less than before, and hence
if C1, one of the telescopes, is moved out of parallel to the other,
through a certain angle, the current through the galvanometer will be
greater than if it were moved through an equal angle out of a parallel
when the telescopes were in the positions C and D. The range indicated
is, therefore, decreased, and by properly proportioning the various
parts it is found that the range can always be read direct from the
galvanometer, or in other words the multiplication of A B/sin( A T B )
by sin( A B T ) is to all intents and purposes performed automatically.
There is, it is true, a slight theoretical error; but by using a small
storage battery and making the contents carefully it is said to be
inappreciable. Each telescope is fitted with a telephone receiver and
transmitter, so that both observers can without difficulty decide on
what point to align their telescopes. It will be seen that it is
necessary that the lines of sight of two telescopes should be parallel
when the galvanometer indicates no current. It has been proposed to
accomplish this by sighting both telescopes on a star near the horizon,
which being practically an infinite distance away insures the
parallelism of the lines of sight.
Rate Governor.
An apparatus for securing a fixed rate of vibration of a vibrating reed.
It is applied in simultaneous telegraphy and telephoning over one wire.
The principle is that of the regular make and break mechanism, with the
feature that the contact is maintained during exactly one-half of the
swing of the reed. The contact exists during the farthest half of the
swing of the reed away from the attracting pole.
Fig. 282. LANGDON DAVIRS' RATE GOVERNOR.
In the left hand figure of the cut, K is the key for closing the
circuit. A is the base for attachment of the reed. V is the
contact-spring limited in its play to the right by the screw S. C is the
actuating magnet. By tracing the movements of the reed, shown on an
exaggerated scale in the three right hand figures, it will be seen that
the reed is in electric contact with the spring during about one-half
its movement. The time of this connection is adjustable by the screw S.
Synonym--Langdon Davies' Rate Governor or Phonophone.