[ 358 ] 
north or fouth limb. Here, indeed, the directing 
wire cannot reprefent a parallel to the equator, on 
account of the moon’s continual change of decli- 
nation, bat will make a fmall angle therewith ; 
which may be computed, and the obfervations cor- 
rected accordingly. But the correction may be ealier 
made, as follows, let a exprefs the moon’s apparent 
angular motion about the pole of the world in four 
minutes ot time, being the difference of her proper 
motion in right afcenfion, and the change of her par- 
allax in right afcenfion: d her apparent motion and 
declination in the fame time, h the difference of the 
apparent declination of the moon, and that of the 
flar, r the radius, and c the cofine of the moon or 
ffar s declination ; the correction to be applied to the 
moon s right afcenfion, or the difference of right 
afcenfion of the moon and ftar is h x - X — . If 
a c 1 
the moon is approaching the ftar’s parallel of decli- 
nation, fhe will come to the horary wire relatively 
too late for the ftar, and her right afcenfion, deduced 
immediately from that of the ftar, will be too great, 
and muft be diminished by the correction here men- 
tioned ; but, if the moon is receding from the ftar’s 
parallel of declination, fhe will come to the horary 
wire relatively too foon for the ftar, and her right 
afcenfion, immediately deduced from that of the 
ftar, will be too fmall, and muft be increafed by the 
above-mentioned correction. 
There is another attention, which the nice ob- 
ferver will not think too trifling for his notice, name- 
ly, to examine whether the wires of his telefcope 
are 
