Weekly expositor. (Brockway Centre, Mich.) 1882-1894, 1892-04-29
VARIOUS. KINDS OF TIME.
Why the watch of u Traveller Going West
Seems to be Fast.
fro BE CONTINUED. I

Why the Watch Of IL Traveller Going West
Seems to be Fast.
Turning upon its axis in the period
which we divide into twenty-four
hours, the sun appears to cross the
meridian OF each place on tho globe
once in that interval. The moment
at which it crosses the meridian of
any place is termed local apparent
noon" at that place. This would all
be very well if the earth and sun re-
NAMED fixed in their relative posi-
tions or II the earth, completing as
1T does an annual revolution about the
sun, did so uniformly in a perfect cir
Gle and that circle were in the same
plane with the motion OF daily rota-
ton. Then the successive intervals
between the meridian passages of the
sun at Greenwich would all be equal
and perfect chronometer set at II
hours, 0 minutes, D seconds. when the
sun passes tho meridian today, would
indicate precisely the same instant
for apparent neon" every day.
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 moro rapid than in another,
causing slight variation in the in
tervals between the solar passages.
Again. the plans OF the earth's path
around the, elliptic is inclined
22I degrees to the plane of the equa-
tor. in which the daily rotation takes
place and consequently twice q year
the intervals OF apparent noon are
each about twenty seconds greater
and twice Il year about twenty seconds
less than twenty-f four hours To ex-
plain just why this result would re-
quiro moro OF an investigation into
astronomical principles than is here
contemplated. but it is so. neverthe-
less. and any text book will elucidate
the reasons. A combination of the
two effects causes tho sun apparently
to slow fourteen minutes in NOvem-
ber But in the course OF year the
average is preserved and therefore q
mean solar day OF exactly twenty
four hours is adopted in the almanacs
and is used for all purposes. This
accounts for the differences between
mean time and sun time. A regulator
keeps the former; a sun dial indicates
the latter.
A few years ago every large city in
the United States had its own local
time, says the San Francisco Exam.
liner. and this was for each place the
true mean solar time. obtained as
above indicated. Consequently man
travelling westward from Washington
would find his watch fast as follows:
At Chicago. AZ minutes; at Omaha,
hour 10 minutes; at Denver hour.
so minutes; ut Salt Lake City 2 hours
20 minutes and finally at San Francis
CO. hours 2 minutes 1t will readily
be recalled how much annoyance both
to trainmen and travellers was occa-
stoned by all these various corrections.
Within the last decade great reform
was inaugurated. To-day traveller
going westward finds his watch fast
from time to time but only the hour
hand is in error. The hour is changed
for each fifteen degrees of longitude.
Washington time Is five hours slow of
Greenwich; Chicago six hours; Den =
yer, seven hours; and San Francisco.
eight hours. All the intermediate
cities and towns are run on one sys-
tenn or the other according to their
location in latitude the standard be-
ing Eastern. Central. mountain and
Pacific time. All the time-pieces on
the coast are set by Pacific standard
time, which is eight hours slow Of
Greenwich mean time. Therefore q
watch which is set at San Francisco
solar time by means OF a corrected
sun dial is still minutes AZ seconds
slower than n Pacific standard time.
because we are that much in longitude
west of the 120th meridian. which
forms the eastern boundary Of North
ern California and on which only Is
! the Pacific time coincident with
'.local mean time"