THE QUARTERLY 
meswRKN AL, (OR  sGit NG E- 
JANUARY, 1875. 
I. THE ILLUMINATED DISC OF THE MOON. 
By Lieut.-Colonel A. W. Drayson, R.A., F.R.A.S. 
Qu 
if the examples which we have given relative to the pole 
alt star and the pointers, the reader’s attention has been 
directed towards the northern portions of the heavens, 
and to those curves and straight lines affecting certain 
phenomena connected with the apparent motion of the 
celestial bodies. We will now call attention to the southern 
portion of the heavens, and refer to those laws which affect 
the apparent position of celestial objects near the Southern 
Meridian. 
In order to comprehend the relative position of celestial 
objects as regards the equator of the earth, it is necessary to 
trace out on the sphere of the heavens an imaginary arch 
or curve which represents exactly in the heavens that curve 
which the equino¢tial (that is the equator produced to the 
sphere of the heavens) actually occupies in the heavens. 
Toan observer situated at the North Pole the equino¢tial 
would be a great circle in the heavens, exactly coincident 
with his horizon. ‘To an observer in 45° north latitude the 
equino¢tial would appear an arch in the heavens, 45° above 
his horizon directly south, and coincident with his horizon 
at the east and west points. To an observer at the equator 
the equino¢tial would appear a straight line, cutting the 
east and west points of the horizon, and passing through 
the zenith. : 
The apparent curve or arch in the heavens formed by the 
equinoctial, as seen from latitude 45° north, can be traced 
out with great accuracy. The altitude of the equino¢ctial 
on the meridian is always equal to the co-latitude; thus 
the meridian altitude of the equinoctial for 45° north latitude 
will be 45°. Taking arcs of the equinoctial of 10°, we 
VOL. V. (N.S.) B 
