Omaha daily bee., 1899-01-07
LARGEST CLOCK IN AMERICA.
II Marks the Passing Hours on Phila-
deIphin's City HnII Tower.


Tue timepiece on the Omaha postoffice
| tower presents a large face to the four
| points Of the compass, but 1t Is far from
| being in the class of the clock on the tower
Of Philadelphias s22, 900 900 city hall, which
! began ticking off the minutes with the new
| year. The faces of the clock are $40 feet
above the sidewalk the highest in the
| world. 1t represents a cost OF s21 900. The
| motive power is compressed air and the vis-
itor to the clock story in the tall tower is
! astonshed to find there are no works" to
| be seen The ponderous hands on the four
| dials are operated by means of air under
| great pressure forced through tubes finer
than telegraph wire, and all four pairs of
hands are controlled by one little master
clock that could easily be set on a library
| mantelpiece
| This little clock, as it ticks the minutes
! received by telegraph from the Washington
| Observatory, in turn releases the compressed
| air, and over each dial 400 pounds OF hands
are pushed forward The hands are moved
| every half minute and the jump of the
| minute hand from half-minute to half
minute Is six and one half inches The
| pressure eXerted is 700 pounds-suffce cent, it
is said to drive the hands under any
weather condition, and neither wind nor
snow nor seet will prevent their accuracy
| at any time.
The motive power applied to this time
| piece is novel one in a clock of its proper
| tlons. Compressed air as a motive power
| has been used before, but all the big clocks
| so far have been operated by means of
| weights. Indeed, Prof. Hardness Of the Ma
| val Observatory at Washington, who was
! consulted before the clock was installed, adj
vised the installation of this method as being
| certain and tried for centuries with success
| He expressed himself as doubling the re,ia-
| bility of electrical appliances as being SUBJ
| Ject to lapses. However, electricity is really
| the power which governs the workings OF
| the clock and by ingenious automatic appli-
| ances 1t is believed that any lapse by cleo
| tricity will be Immediately taken up by the
| relief motors etc
| There are two electric motors used to work
| the pumps to compress the air, and so ar
| ranged that in the event of one breaking
| down the other will Immediately take its
| place without fraction Of time intervening
Should the other fail also water motor will
assume its work The only thing that has
not been provided against is a break in the
Illuminating circuit. That, however, is
| tritling matter compared with the accuracy
and constancy of the clock.
This same idea of having all the work
| done by machines that will instantly come to
| the relief of the other is carried out with
| the master clock the heart and brains, so to
speak, of the Brobdingnagian timepiece,
which has also it's fellow These master
clocks are expected to vary less than ten Sec
onds week. The big one consequently,
will be just as accurate.
These master clocks are located in a room
on the seventh floor of the city hall. 200
| feet below the big dials in a glass COM
partment in which the temperature is kept
always, by means of thermostat and cleo
trio coils, at rs degrees. Even in summer
| it is not believed this heat will be ex
ceeded. Both of the master clocks are not
connected constantly with the pneumatic
apparatus which moves the mechanism of
| the big clock. Only one is employed, but
! the other could be connected Immediately
should any failure be noticed.
| The master clock regulates the flow OF
| compressed air. This Is conveyed in tubes
| to a receiver, whose diaphragm. operating
| upon a pawl through two or three gears,
gives an effective push of 700 pounds on a
rachel wheel and moves the minute hand
every half minute The motion is conveyed
by perpendicular shaft and bevel gear to
! the center of the dial, where it is trans
| mitted to the hands The rachel wheel Is
similar to that in the ordinary clock, one
| pawl holding the wheel until the other paw
| pushes it forward. The diaphragm filled
with a supply of compressed air, pushes
| the hands forward gradually the first half
| of the minute, and at the same time has
compressed certain springs, which, in turn,
push the other pawl as the valve is opened
| and lets the charge of air escape While
| there are thus two motions minute, the
action is gradual, and not jerky, being as
| evenly worked as the movement in watch
| Another popularity OF the clock is the
! absence of figures on the dials, broad strips
Of bronze taking their place. These are OF
| uniform width, excepting those taking the
| place of III, W. TX and XII, which are an
| inch wider, for sake of convenience. These
strips are feet 2 inches long and 13 inches
! broad. Each hour hand is 0 feet long and
fet inches broad, and weighs 175 pounds
| each and each has an extreme length of
16 feet, for each is counterbalanced. Each
dial complete, fitted with its nnety-two
| pieces Of glass, weighs five TONS One fve-
minute section, for so the dials are con-
structed, weighs 525 pounds.
| The problem Of illumination was one OF
| considerable difficulty, but it is believed it
has been solved successfully. The central
| part of each dial is divided into four circles,
| feet 7 inches in diameter, into each OF
| which is fitted single piece of glass.
|