The Dawson news. (Dawson, Ga.) 1889-current, 1892-01-20
POINTS ABOUT TIME.
VARIATIONS AND THE CAUSES WHICH
PRODUCE THEM.

The Earth's Revolutions on Its Axis, To-
gether with Its Journey Around the
Sun, Are the Disturbing Factors-No
Watch Is Perfectly Reliable.
If there is one single scientific problem
upon which more than another people
appear to get mixed that problem is
time. Standard time, local time sun
time are exceedingly difficult problems
for the public to puzzle over, and when
sidereal time enters the calculation the
case is hopeless indeed. | have FIRE.
quently of late seen so many letters ad-
dressed this and other journals, all
touching upon one or the other of these
chronological questions, that have CON
cluded a short note explaining the main
points of difference would be, at any
rate, timely. If it only suggests to the
young men in the business offices the
idea Of going to work at a. m, local
mean time, and leaving off promptly at
p. m, Pacific standard time, the ques-
ton will have been shown to possess Il
practical side. The application of it,
however, is purely a matter of taste.
Well, to come to time, the great chrO-
nOmeter and regulator in chief to the
business, social and scientific world is the
earth itself Turning upon its axis in the
period which we divide into twenty-four
hours, the sun appears to cross the me
ridian of each place on the globe once in
that interval The moment at which it
crosses the meridian of any place Green
wich), for example, is termed ''local ap-
parent noon" at that place. This would
be all very well if the earth and sun re-
manned fixed in their relative positions;
or if the earth, completing, as it does, an
annual revolution about the sun, did so
uniformly in perfect circle and that
circle were in the same plane with the
motion of daily rotation. Then the sue
cessive intervals between the meridian
passages of the sun at Greenwich would
all be equal, and perfect chronometer
set at u hrs, min, 0 Sec, when the
sun transited today would indicate pre-
cisely the same instant for apparent
noon" at every date.
MOTIONS OF THE EARTH.
But the earth's path around the sun is
not perfect circle; it is an ellipse, and
the motion in one portion of the ellipse is
more rapid than in another, and this
causes a slight variation in the intervals
between the solar passages. Again, the
plane of the earths path around the sun,
or the elliptic, is inclined 2315 dogs. to
the plane of the equator in which the
daily rotation takes place, and conse-
quently twice a year the intervals Of
apparent noon" are each about twenty
seconds greater and twice year about
twenty seconds less than twenty-four
hours. To explain just why this results
would require more of an investigation
into astronomical principles than is here
contemplated; but it is so, nevertheless,
and any text book will elucidate the rea-
sons. A combination of the two effects
causes the sun to be apparently slow
fourteen minutes in February and fast
sixteen minutes in November. But in
the course Of a year the average comes
out all right, and therefore ''mean
solar day of exactly twenty-four hours
is adopted in the almanacs and used for
all purposes. This accounts for the diff
ference between mean time and sun time
A regulator keeps the former; sun dial
indicates the latter.
A few years ago Tor prior to 1880 every
large city in. the United States had its
own local time, and this was for each
place the true mean solar time, obtained
as above indicated. ...'..
REGULATING TIME.
Consequently, man travelling west
ward from Washington would find his
watch fast, as follows At Chicago, AZ
minutes ; at Omaha, hour 16 minutes;
at Denver hour SO minutes; at Salt
Lake City, hours 90 minutes, and final
ly, at San Francisco, hours . minutes.
1t will readily be recalled how much
annoyance was occasioned by all these
various corrections, both to trainmen
and travellers About the year men
toned a great reform was inaugurated.
Nowadays traveller going westward
finds his watch fast from time to time,
but only the hour hand is in error. All
the clocks in the country Indicate the
minute and second of Greenwich mean
time, but the hour is changed for each
10 dogs. of longitude. Washington time
is hours slow Of Greenwich; Chicago,
hours; Denver, hours. In San Fran
cisco we are hodrs slow of the prime
meridian. All the intermediate cities
and towns are run on one system or an
other, according to their location in
longitude, the standards being eastern,
central, mountain and Pacific time. All
the time pieces on the coast are set by
Pacific standard time, which is s hours
slow of Greenwich mean time. There
fore, watch which is set at San Fran
cisco solar time by means of a corrected
sun dial is still 8 minutes AZ seconds
slow of a Pacific standard time clock,
because we are that much in longitude
west of the 120th meridian, which forms
the eastern boundary of northern Cali
fornia and on which only is the Pacific
time coincident with local mean time.
San Francisco Examiner