DA Y. 
if the earth moved in a contrary direCtion, the fidireal day 
would exceed the folar day. 
On the contrary, in the month of January, the earth being 
in that vart of its orbit neareft the fun, moves qu uicker, and 
the excefs of the 
To explain the effe& of the fecond caufe, it mult be ob- 
ferved that this excefs of the eee er + abrSnomia day i is mea- 
parent motio nin the ec- 
liptic to the equator, on which es we 2 always ete the 
a motion “ the earth round i its axis 
two great cir reles of the ieee to Ri 
rial day. at the equinoxes this {mall are of the equator 
will be lefs than the correfponding arc of the ecliptic in the 
ratio of the cofine of the eee of the ecliptic to radius ; 
but at the folftices it is greater in the ratio of the radius to 
the obliquity. The folar day j is therefore diminifhed in 
the firft cafe, and augmented i inthe fecond. The method of 
ee ating the precife effe& of thefe inequalities will be 
given in the article eee on of Time. 
o obtain a mean day independent of thefe caufes, we 
may fuppofe a fecond fun moving uniformly along t 
ecliptic, and traverfing the greater axis of the ellipfe, at cn 
fame infant with the true fun: this pili will oa - 
inequality arifing from the proper motion 
The inequality arifing from che obliquity of 
the eae may be lisewife removed by imagining a third 
ua 
elapfe between two eee tranfits of this imaginary 
fun over the meridian, conftitutes a mean folar day. 
ime ig meafured by the number of thefe imaginary 
True time by the tranfits of the real fun. 
The unequal length ‘of the days and nights in different 
climates, or in the fame climate at different feafons, is another 
effect of the inclination of the earth’s axis to the plane of its 
rbit. 
If the e ee coincided with the ates the circle 
bounding light and darknefs would ane divide th 
and all its pale wen two equal part 
But 
equal day and night y where throu Shai e year. 
by the oe oe ne axis, the equator ane remains bi- 
fected as ey ie all the other circles unequally divided 
except on of the equinox. After which, one 
ole with its adj aol circles will be radually plunged into 
total obf{curity, aud the oppofite pole with its circles brought 
out into conftant light. 
At the folftices the portion of total obf{curity, and con- 
ftant illumination, will extend from the poles a number of de- 
grees equal to the obliquity of tte ecliptic. 
he length of the day in any latitude, at any feafon, 
be found by the {olution of a right angled a aaa tingle 
in which the diftance of the fun d the al- 
aad the latitude of the pac P 0, 3 are given, The. ae 
aaa ed © PO, or more properly its complement ZPO, 
s the fem‘diurnal arc, or the time elapfed from fun-rife to 
aco or from noon to fur-fct. 
Nations have mn munch from each other as to the 
commencement, and ftill more in the neha of the d 
The Chaldeans, Syrians , Perfians, and ians began the 
day at fun-rife, and divided both the day and nights into four 
This divifion of the day into quarters w ufe lon 
adopted in moder: Europe. 
civil day at midnight, and derived this pr 
ancient jurifprudence, and rites of religion, eftablifhed tong 
before they had any idea of the divifion into hours. Ac- 
cording to Varro, the firlt fun. dial {een at aa was pei 
from pie in cet in the firft Punic 1 s part of the 
It was aoa vl % in the ‘forum, 
. oo tude of 
conftruétion. The Greeks divided the na- 
yi {2 hours, a practice, which according to He- 
— | derived from the epee Thefe hours 
ere of c 
man republic, and of Plutarch and othe 
under the emperors; and fuch they continued at Conttanti- 
nople, when the weftern empire was no more alladius, “de 
re ruftica,”’ gives the hutbandman a eras of hours, and 
teaches him to diltinguifh them in every month of the yeary- 
by the length of a fhadow projeéted by a perpe eee ar pole. 
This fhadow decreafes from the = ‘ . the fixth ae when 
it is fhortett; it then increafes Att ft hour 
in the morning and the ee in “the afternoon abe makes 
it always equa “pus when Plin rrects that apples in 
autumn = d not gathered, Ante heramn priman (Nat. 
Hitt. i v. cap. xviii.) he means til they” have h 
hour’s fu a them. Vhe nocturnal hours w 
in the fame manner as thofe 
the fixth hour of the night. pears from a neilage in 
b 
Varro, that an officer called acceufus, ufed, by order of the 
retor, to procisim the third hour, mid-day, end the ninth 
hour. Thefe divinons of the natural day into four parts were 
called vigils, the firtt beginning at [un rife, the fecond at the - 
third hour, the third a = -day, and the fousth at the ninth 
‘g 
hour. ‘lhe night was in the fame manner divided into four 
vigils. And eas the — empire at this day, 
time 15 rec y certain porcions of the natural day, ree- 
one 
fembling the vigils of the ancient Jews and al sac 
time are 
Their principal jpalion of ie 
natural day is into four-parts, ane are unequal at different 
feafons, and in different parts of the empire. 
re ca no doubt but ae men of f{cience among 
€ ancients were acquainted sb pile ours. Pliny calls 
ten equinoxial hours. ufed in aflronomical cal- 
culations, for computing the me a the fay in if erent cil- 
mates and feafons. In Egypt likewife the d 
nequal hours. Ptolemy marks tie tim ae Ae (ae ne 
nomenon, by chefe as well a3 equa cone. to accommodate 
his 
