P R E 
Wives of the eldest 
sons; daughters, b 
Wives of the eldest f of Knights of the Gar- 
sons ; daughters, ) ter. 
Wives of the eldest ? of Knights of the 
sons; daughters, S Bath. 
Wives of the eldest ) Knights-Bachelors. 
sons; daughters, b 
Wives of the youngest sons of Baronets. 
Wives of Esquires, by creation. 
Wives of Esquires, by office. 
Wives of Gentlemen. 
Daughters of Esquires. 
Daughters of Gentlemen. 
Wives of Citizens. 
Wives of Burgesses, &c. 
The wives of Privy Counsellors, Judges, 
&c. are to take the same place as their hus- 
bands do. See the former list. 
PRECENTOR, a dignitary in cathe- 
drals, .popularly called the chantor, or mas- 
ter of the choir. 
PRECESSION of the equinoxes, is a very 
slow motion of them, by which they change 
their place, going from east to west, or 
backward, in antecedentia, as astronomers 
call it, or contrary to the order of the signs. 
From the late improvements in astrono- 
my it appears, that the pole, the solstices, 
the equinoxes, and all Ae other points of 
the ecliptic, have a retrogade motion, and 
are constantly moving from east to west, 
or from Aries towards Pisces, &:c. by 
means of which, the equinoctial points are 
carried further and further back among the 
preceding signs or stars, at the rate of 
about 50 '^ each year ; which retrograde mo- 
tion is catted the precession, recession, or 
retrocession of the equinoxes. 
Hence, as the stars remain immoveable, 
and the equinoxes go backward, the stars 
will seem to move more and more eastward 
with respect to them ; for which reason the 
longitudes of all the stars, being reckoned 
from the first point of Aries, or the vernal 
equinox, are continually increasing. 
From this cause it is, that the constella- 
tions seem all to have changed the. places 
assigned to them by the ancient astrono- 
mers. In the time of Hipparchus, and the 
oldest astronomers, the equinoctial points 
were fixed to the first stars of Aries and 
Libra ; but the signs do not now answer to 
tlie same points ; and the stars which were 
then in conjunction with the sun, when he 
was in the equinox, are now a whole sign, 
or 30 degrees, to the eastward of it: so, 
the first star of Aries is now in the portion 
of the ecliptic, called Taurus ; and the stars 
PRE 
of Taurus are now in Gemini ; and those of 
Gemini in Cancer ; and so on. 
This seeming change of place in the stars 
was first observed by Hipparchus of Rhodes, 
who, 128 years before Christ, found that 
the longitudes of the stars in his time were 
greater than they had been before, ob- 
served by Tymochares, and than they were 
in the sphere of Eudoxus, who wrote 380 
years before Christ. Ptolemy also per- 
ceived the gradual change in the longitudes 
of the stars ; but he stated the quantity at 
too little, making it but 1° in 100 years, 
which is at the rate of only 36 " per year. 
Y-hang, a Chinese, in the year 721, stated 
the quantity of this change at 1“ in 83 
years, which is at the rate of 43' i per year. 
Other more modern astronomers have made 
this precession still more, but with some 
small differences from each other ; and it is 
now usually taken at 50 per year. All 
these rates are deduced from a comparison 
of the longitude of certain stars, as observed 
by more ancient astronomers, with the later 
observations of the same stars ; viz. by sub- 
tracting the former from the latter, and 
dividing the remainder by the number of 
years in the interval between the dates of 
the observations. Thus, by a medium of a 
great number of comparisons, the quantity 
of the annual change has been fixed at 
50"i, according to which rate it will re- 
quire 25,791 years for the equinoxes to 
make their revolutions westward quite a- 
round the circle, and return to the same 
point again. 
The phenomena of this retrograde motion 
of the equinoxes, or intersections of the 
equinoctial with the ecliptic, and couse- 
quently of the conical motion of the earth’s 
axis, by which the pole of the equator de- 
scribes a small circle in the same period of 
time, may be understood and illustrated as 
follows ; Let NZSVL be the earth. (See 
Plate Perspective, &c. fig, 6.) SONA its 
axis produced to the starry heavens, and 
terminating in A, the, present north pole of 
the heavens, which is vertical to N, the 
north pole of the earth. Let EOQ be the 
equator, TffiZ the tropic of cancer, and 
VTVJ the tropic of capricorn ; VOZ the 
ecliptic, and BO its axis, both of which 
are immoveable among the stars. But as 
the equinoctial points recede in the eclip- 
tic, the earth’s axis SON is in motion upon 
the earth’s centre O, in such a manner as 
to describe the double cone NOn and SOs, 
round the axis of the ecliptic BO, in the 
time that the equinoctial points move round 
