Å |CASTRONOMICAL anp 
ing points of the equator and ecliptic. Let the are 6Zi repre- 
. fent the latitude of fome given place ; then the point Z, where 
the arc is interfe€ted by the meridian, is the zenith of the place, 
at the given time, and is one of the poles of the horizon ; the 
arc HOR is the horizon ; the line ZN its axis, and the point 
N of the axis, where it is interfected by the arc Pc S continued, 
is the other pole of the horizon, or the nadir. "The arc ?ZL, 
drawn through the poles of the ecliptic and of the horizon, 
marks out the longitude of the nonagefimal degree upon the 
ecliptic at U, the altitude of which, or height above the hori- 
zon is VU. Now the arc pZL is perpendicular both to 
the horizon and the ecliptic, as it paffes through the poles of 
each, and as pU is = ZV = go? and ZU is common to 
both, take ZU from each, and there will remain pZ — VU 
the altitude of the nonagefimal degree of the ecliptic. ‘The 
longitude and altitude of this point, therefore, may be readily 
found by the fpheric triangle PpZ, in which are given two 
fides and the included angle, viz. fide PZ = the co-latitude 
of the given place; the fide Pp — the diftance of the poles 
of the equator and ecliptic = the obliquity of the ecliptic ; and 
the angle pPZ, the value of which may always be determin- 
ed by the following general rules, which, from diagrams, will 
appear very obvious. 
The right afcenfion of the mid-heaven being between 270° 
and 360° or o^, and between o^ and go°, the neareft equinoc- 
tial point is + ; ; and in the firít cafe, angle pPZ is acute, and 
is found by fübftra&ting 270° from the right afcenfion of the 
B mid-heaven. In the fecond cafe, the angle is obtufe, and is 
found by fubftra&ing 270? from the right afcenfion of the 
mid- 
We ey cea MERE e cer 
