238 
POPULAR SCIENCE REVIEW. 
time and some skill. But if conveniently attainable, thejr 
would add materially both to the accuracy and the effect of 
the resemblance. It is true that in consequence of the ex- 
treme tenuity of the lunar atmosphere, there is an entire 
absence of that diffusion and softening of light which so espe- 
cially characterises the terrestrial landscape. With a daylight 
sky, resembling probably that of our midnight, and devoid of 
the mists of sunrise or sunset, every spot where the sun is not 
actually shining would of course be shrouded in intense black- 
ness of shade ; but there are abundance of banks and slopes 
lying in planes which intersect the solar disc, and consequently 
receive a partial or penumbral illumination, contributing 
greatly to the varied effect of the landscape, and to the truth 
and certainty of its relief. And the more fully these are ex- 
hibited in any mode of representation the better. 
A very little experience in drawing will convince us of the 
expediency of confining ourselves to a limited area. It is very 
desirable not merely to be able to complete what we have 
undertaken, but to avoid the change of effect inseparable from 
a delineation protracted through many consecutive hours. 
The alteration in the amount of shadow, especially near the 
terminator, during a winter’s evening, would strike an unaccus- 
tomed observer with surprise. 
With respect to the choice of regions suitable for represen- 
tation, especially for the commencing student, those approach- 
ing to the limbs must take decidedly the last place. Not only 
is the perspective foreshortening likely to cause perplexity and 
mistake among unknown objects, but, owing to the never- 
ceasing action of libration, that foreshortening is in a state of 
continual restlessness. Every night we look upon a fresh limb ; 
a similar aspect is slow in its return ; entire correspondence 
is not restored till after three years ; and during the brief 
period of its continuance he must be a novice indeed in actual 
work, who would flatter himself, at least in an English sky, 
with the hope of similar atmospheric conditions. Eegions 
near the centre of the disc are far more suitable, especially for 
early efforts ; but it must not be forgotten that even such 
districts are not altogether free from the displacement occa- 
sioned by libration, and its effect in changing the relative 
proportions and situations of objects ought to be studied and 
allowed for. In fact a clear understanding of this cause of 
apparent variation must underlie any satisfactory investigation 
of the interesting enquiry already referred to, whether the con- 
vulsions which have in former ages shattered the superficies, 
of the lunar globe have now sunk into entire quiescence, as 
well as that scarcely less curious question, whether physical 
change may not be detected, on or immediately above the 
