Evening star., 1922-07-23
Curious and Ingenious
Clock Construction

AIOCk SOnSIfuCtlOn
IN the case of clocks of precision.
used by astronomers and physi-
cists. some interesting and ingenious
| applications have been made of nickel
steel and of electro Undue
| tion for the maintenance and regis
tration of oscillations
The employment of "invar," which
| s36 per cent nickel-steel. the ex-
pansion of which may easily be made
lower than one-fifteenth that Of steel.
has rendered easier and more exact
the compensation for variations in
the length of the pendulum, due TO
temperature. This compensation is
obtained simply by the upward ex-
pansion of the steel bob, which is
attached to the stem by its lower
edge.
Such clock is placed in a case at
constant pressure and in a place
where the temperature varies little
varies only by an insignificant frac-
tion of a second each day. Cnfortu-
nately. the devices for maintaining
and registering the motion introduce
perturbations, owing to the necessary
friction. which. feeble though they
may be. are irregular and cause the
length Of the oscillation to vary. 4.
An attempt has been made, though
for some time with little success, to
use electricity to actuate or connect
these various mechanisms. In gen
eral, the device used was an electro
magnet, which. being excited at each
oscillation, returned to the clock,
either directly or not, its lost energy.
For this it was necessary to make
contact with the clock itself, and this
gave rise to friction. This has been
shown in a very curious way by plac-
ing in the circuit a telephone IN
which the noise Of the contact could
be clearly recognized. Now. how
ever. by very delicate special devices
it has been possible to abolish fric-
ton altogether ana thus to obtain
clocks that keep time to about one
tenth second a day. Th' best sys-
tenn. it is thought, is thaA devised oy
Ferry, which is said to do bway alto
gether with any material connection
with the pendulum, except. of course.
the suspension. for which a thin, nat
piece of flexible metal is used. The
stem is of "invar" and supports
horizontal horseshoe magnet, as well
as An additional mass serving for
regulation. At each oscillation one
of the branches of the magnet enters
a bobbin connected with a battery.
while the other enters a copper ring
suspended by a wire and constituting
pendulum of the same period OF
oscillation. The ring is carried along
by the magnet by the action of the
currents induced in it by the latter.
] but is always a quarter of an oscil-
| lation behind it. This second pendu-
lum makes the contact closing the cir
cult between the battery and the bob
bin that attracts the magnet.
This clock starts as soon as the bat
| terry circuit is closed and assumes,
without. regulation, a steadiness OF
oscillation that seems never to have
been reached before.
The school clock made by NJ. A.
Poitel of Grenoble constitutes a par
ticularly attractive one for the shop
window. 1t is made to represent the
old type of schoolmaster who, with
stick in hand, used equally for teach
ing and chastisement. is instructinE
an urchin in what appears to be
sum in arithmetic, but the figures
really represent the hours, to which
the teacher automatically points as
the movement impels his arm to In
dicate the passage OF time.
La mappenmonde" (the map Of the
| world) is the name of another in
| eenious mechanical device, the inven-
ton of a clockmaker of Bethune. The
movement is in the interior OF the
globe and causes it to revolve and
80 mark off the hours on the equato-
rial band by means OF a locomotive,
which, by the. way, has separate
mechanism of its own whereby. II
the globe is made stationary. it may
make a circuit on its own rails OF
the EQUATOR in twelve hours.
! II the clock is used for show pur-
poses, the stationary locomotive with
revolving globes is possibly the best
method to employ. as the locomotive
may then be kept always in view oil
the public, but as an ingenious and
useful clock for private use the cir
cuit made by the locomtive is more
interesting.