Richmond times-dispatch. [volume] (Richmond, Va.) 1914-current, 1919-09-28


the same in the morning a: IN tss evening
81. c. Providence. r. u
Tho difference is due 70 tho adoption
J. of the clock in tho place Q! the sun 10
regulate our rcckoneinE q :i7nc. The
apparent motion OF the sun through
the sky determines thc duration %
daSliEht, bat this varies u conse-
auence OF two principal causes: hrst
the variation in the speed OF the
earth's motion around the sun ~ diff
fercnt se,sons-tastcr III winter. when
il is nearest the sun. and slower in
sunlmcr-ard second the cfTeC; Of the
obliquity OF the ecliptic or the incIina
ton of the carths orbit % the plane
of its equator. which produces another
variation III the rate Of the suns APP
parent motion.
II is not possible TO make these. clear
without the aid OF mathematical dia
grams or celestial globe, bui tho
combined effect OF the TWO causes is
TO make sun tiUe. which is shown by
sundial run now ahead and now be-
hind clock time. which is theoretically
unvaryine.
Clock time is called mean sun or
mean solar time because IL is set TO
follow the movement Of an imaeinary
sky from East 10 West At a perfectly
uniform rate a; all seasons.
rimc sun Governs Day.
However, it is the true sun and not
the imaginary or mean sun that SOW
erns the length OF day and night and
so when we want 20 know the actual
facts about time we use a table calcu-
lated 10 show al a glance when and
behind the sun. -Four times every year,
viz, about April IL. June IA, Scptem-
BIER and December -. the clock and
the sun are in accord: From December
until April the clock is ahead: from
April to- June the sun is ahead; from .
June 10 September the clock is ahead
= ~ nd G. ,I..N,- NJ,
Der the sun leads the clock.
The maximum differences occur unc
middle Of February. when the sun rs
nearly fifteen minutes behind, and tbs.
first OF November. when the clock is
about sixteen minutes behind There
are two minor maxima. viz.-thc mid
minutes ahead, and the end of July,
when the clock is six or seven minutes
differences are prorort.onaly smaller.
i now remains TO exn.ain how these
d,hsrencos affect nc restrictive lengths
Will lie Past Meridian.
:. Suppose we begin with the first OF
November. when tho sun is a quarter
Of an hour ahead Of the clock. Now.
note that sunrise and sunset are cal
culated for the real sun but the time
rs mean sun or clock time. Consequent.
y when the clock. about The mrs, Of
November, marks noon. tho sun, which
rose quarter OF an hour ahead of the
clock. will he by so much past the
SneTluldn OF lne noon INC. nat nlucn
time: then. appears to have been added
10 the forenoon half OF the day and
since the sun will set a quarter of an
hour ahead of mean time. the same
amount will appear TO be subtracte;i
from the afternoon.
This difference becomes less and less
until about Christmas Day. when Iho
Two times are in accord But after
Christmas the afternoon app.ars 10
lcnCthen at the expense Of the fore
noon. because now tho sun falls be-
hind the clock more and morc, until
Its maximum rctardati0n in February
and then less aud less until all diff
ference again disappears IN the middle
OF April
Forcnoons Longer in juno.
From the middle OF April till the
middle OF June the forcnoons arc
longer: from the middle of June till the
beginning OF september the afternoons
ming of September tho afternoons have
the majority, and from thu beginning
of September until Christmas the fore
moons once more forge ahead.
The difference between the two
the clock is usually more noted
during the weeks that most immc-
diatc,y precedc and follow Christmas.
because then the earth makes its peri
helion swing through that part OF its
orbit nearest the sun, where its speed
i9 increased.
H. is hardly necessary Ia point out
that wh,n VIC arbitrarily set our clocks
an hour ahead OF mean sun time We
throw The dividing line between fore
end Of Jxfy the s.su,. is SLOW about u" six six
minutes. and the afternoon. by mean
clock time, is twelve minutes longer
than the forenoon. but under Wight
saving tho afternoon exceeds the
forenoon by two hours and twelve
minutes.
ESE e "a EQ "A = "a NR