6 The Illuminated Disc of the Moon. (January, 
be a line coincident with a straight line joining the sun and 
the moon. 
In these two examples the right hand side of the moon has 
been given as the illuminated side; exactly the same laws 
will hold good when the left side of the moon is illuminated, 
the most marked effects being visible when the moon is go” 
distant from the sun, and when the sun and moon are 
equally distant from the horizon, and the observer is at or 
near 45 latitude. 
It may be difficult for those individuals who are not gifted 
with great powers: of observation to perceive that the 
pointers sometimes point more directly towards the pole 
star than they do at other times. We believe, however, 
that this faét is one which merely requires attention to be 
directed to it, after which it will be perceived. 
The phenomenon connected with the illuminated disc of 
the moon is one which does not require such careful obser- 
vation as does that relative to the pole star and the pointers: 
very average observation will enable a person to note the 
facts to which we have called attention relative to the illu- 
minated portion of the moon’s disc that is turned towards 
the earth. Thus, if the reader either does not understand 
the demonstrations here given, or doubts their accuracy, he 
can examine the fact for himself, and if he select the suitable 
conditions, he can twice a month observe the phenomenon 
in the heavens. The best time to note the fact is when the 
moon is in either the first or the last quarter, and when 
consequently she is half illuminated. If the moon be illu- 
minated on the west side, that is during the first quarter, 
the best time to observe the effect is at 3 P.M. If the 
moon be illuminated on the left or east side the best time 
will be 9 A.M. The winter time is better than the summer, 
because during winter the moon’s light enables her to be 
better seen than during the summer. 
The same geometrical laws of the sphere which cause the 
pointers to alter the direction in which they point relative 
to a fixed star, also cause the line of light and shade on the 
moon to appear sometimes not.at right angles to the line 
joining the moon and the sun. It is a singular law, but it 
is one not without interesting results. 
Singular as it may appear to some readers, yet it is a 
fact that not one individual out of one thousand to whom 
we have spoken on the subject has ever remarked that the 
pointers did not always appear to point to the pole star, and 
scarcely one person in a hundred has ever remarked that 
appearance of the moon when half illuminated which we 
