Weekly expositor. (Brockway Centre, Mich.) 1882-1894, 1892-05-06
VARIOUS KINDS OF TIME.
Why the Watch of q Traveller Going Yves,
Seems to be Fast.

Why the Watch of Traveller Going wea
Seems to be Fast.
Turning upon its axis In the period
which we divide into twenty-foul
hours, the sun appears to cross tn,
meridian OF each place on the globe
once in that interval. The moment
at which it crosses the meridian oil
any place is termed ''local apparent
noon" at that place. This would all
be very we'll if the earth and sun re-
manned fixed in their relative posi-.
tions: or il the earth, completing al
1T does an annual revolution about thd
sun. did SO uniformly in perfect cir.
Gle and that circle were in the same
plane with the motion OF daily rota!
tion. Then tho successive intervala
between the meridian passages of thd
sun at Greenwich would all be equal
and " >,sr'ect chronometcr set at II
hours, u minutes D seconds. when the
sun passes the meridian today. would
indicate precisely the same instan,
for apparent neon" every day.
But the earth's path around the sun
is not perfect circle; it is an ellipsc.
and the motion in one portion OF the
ellipse is moro rapid tnan in another,
causing slight variation in the in.
tervals between the solar passages.
Again the plans OF tho earth's path
around the. elliptic is inclined
224 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 i"enty seconds greater
and twics year about twenty seconds
less than twenty-four hours. 10 ex-
plain just why this result would re.
quire more Of an investigation into
astronomical principles than is here
contemplated. but it is SC neverthe-
less. and any text book will elucidate
the reasons. A combination OF the
two effects causes tho sun apparently
to slow fourteen minutes III Novem-
Der. But in the course Of year the
average is preserved and therefore a
'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, maa
travelling westward from Washington
would find his watch fast as follows:
At Chicago AZ minutes; at ON aha,
l hour. 10 minutes; at Denver, hour,
so minutes; at Salt Lake City, hours,
20 minutes and finally at San Francis.
co. 3 hours 2 minutes. 1t will readily
be recalled how much annoyance both
to tranmen and travellers was occa.
stoned by all these various corrections.
Within the last decade great reform
was inaugurated. To-day a 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; Dem
ver 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, tho 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. There ore a
watch which is set at San Francisco
solar time by means of n corrected
sun dial is still minutes AZ second,
slower than Pacific standard time,
because we are that much in longitude
west of the 10th meridian, which
forms the eastern boundary of North.
ern California and on which only is
the Pacific time" coincident with
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