Audubon Republican. [volume] (Audubon, Iowa) 1894-1925, 1919-05-22
PROCESS USED FOR TURNING
UP CLOCK. TUESDAY, APRIL

Advancing of clock hands to per-
NIT daylight saving" has created
much interest in the manner in
which accurate records of the time Is
kept throughout the country.
J How accurate time Is taken from
| the stars, at the Illinois Watch Co.
astronomical observatory, is told in
the current issue of "Doings' the
| Joint publication of the watch fac
! tory and the Sangamon Meter Co.
The article, in part, follows:
| Thine is a measure of duration.
/ We measure IL in various ways.
Take, for instance "a day. This is the
time il takes the earth to rotate
once on its axis. With reference to
the sun we call this rotation solar
day; with reference to any fixed star
sidereal day A year consisting Of
1865 Y days is the time it takes the
| earth to make one revolution in its
orbit around the sun.
"The first mQtion' of the earth
causes day andTmght, the second,
the changing of the seasons. These
revolutions, then, give us our idea
of the passage of time But the sun
standard is rot an accurate one. For
six months of the year the sun is
south of the equator, while during
the other six months 1t is north of
it. Twice in the year-at the equi-
notes.-the sun crosses the equator
and we have days and nights Of
equal length Twice in the same
period the sun is farthest north and
| farthest south and we have the long
est and shortest days of the year.
Reference to the following table of
sun and clock time will show that on
February 10 sun time is Is min
utes slow; May IA sun time is four
minutes fast; July 25 sun time is
six minutes slow; November End sun
time is 16 minutes fast.
SIN the earlier ages the sun time
standard answered every purpose.
But it is not sufficiently accurate for
the age in which we live. We must
have an unvarying standard, one
that is absolutely the same on every
point of the globe. That's why we
take our time from the stars.
Longitude is reckoned from
Greenwich and its meridian is mark
ed zero. Springfield's longitude is
SO degrees, 3S minutes, 33 seconds,
or nearly 80 degrees west. As there
is a difference OF one hour in time
for points every Is degrees east or
west of Greenwich our central stand
ard time is six hours earlier than
Greenwich The exact time on our
meridian given above is five hours,
So minutes and 34.2 seconds earlier
than Greenwich. All that is need
ed then, to determine local time is
to observe the passage of any OF the
fixed stars over the meridian at
Springfield and to note the time of
crossing by sidereal clock. The
object of the star observation is to
determine the error of the sidereal
clock This done, the error of the
mean time clock is easily found by
simple formula which reduces
mean time to sidereal time.
"These observations are made
through a transit, a small telescope
set in the east room of the observa-
tory. This instrument swings on
the meridian and can be directed
toward any star which crosses II
whether north. south or overhead as
the observatory was built with open
ings for this purpose
"In the eyepiece of the transit we
find a series of vertical spider lines
as well as several horizontal ones.
The observer turns the telescope to
the altitude where the particular
star he has in mind will cross the
meridian. AS the star crosses the
various spider lines he touches the
key shown in the front of the instru-
ment. This key-is connected with
the chronograph which records sid
ereal time by one pen while the other
pen records the time of the stars
crossing of our meridian. Each
span marked by these pens on the
chronograph is half inch in length
and measures Just a second of time.
Each time the key is touched to re-
cord the crossing of star the pen
connected with the key Jumps"
When the observation is concluded
the space between the marks made
by the sidereal clock pen and the OBJ
servation pen are measured by rule
divided into hundredths of an inch.
GAS each pen covers half inch of
space in a second, difference of
100 of an inch between the
Jumps" indicates that the sidereal
clock is just 2-100 of second fast or
slow. These observations are TAX
en- daily and afford an unvarying
standard by which our master clocks
are kept regulated and these in turn
supply the standard which is so rig
idly followed in adjusting and tim
ing of Illinois watches"