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of libration between tlie spectator and tbe true end of the 
shadow, or are again removed out of the line of sight ; a varia- 
tion which it will readily be seen affects still more extensively 
the apparent breadth of shadows in these positions. Again, in 
certain cases shadows may vary in breadth and direction, or 
even visibility, according to the lunar change of season ; for 
this, though small in extent, the axis being inclined only 
1° 32' 9", may not be always imperceptible. It causes so much 
■difference in the points of lunar sunrise or sunset, that a straight 
face of cliff running E. and W. might at one time be made 
visible by casting a broader, at another by a narrower shade ; 
. at another season, might be undistinguishable ; at another, 
might come out as a white streak from being exposed to sun- 
shine. And this real difference in illumination might, again, 
be masked by change of libration, if this happened to turn such 
a face of cliff, whether in sunshine or in shade, towards or from 
the spectator’s eye. So the black spire projected by an insu- 
lated mountain may in some lunar seasons be carried fully out 
to its tapering extremity, passing close by the side of a hill, 
which at another time a slight change of direction in the solar 
rays brings right into its course, so as to shorten and square it 
off ; and so, too, the brilliant point encompassed by darkness 
which denotes a summit on the night-side just touched by the 
rays of the rising or setting sun, may be visible or invisible at 
different times from a similar cause, the altered bearing of the 
sun in the lunar sky at one time throwing over it, at another 
beside it, the shadow of some object near the terminator. Other 
similar cases of illusion might be named. The end of a shadow 
may be apparently prolonged by its falling into a depressed and 
already darkened spot ; or its form may be suddenly changed 
from pointed to round if the extreme apex cast from some 
sharp and prominent “aiguille” should, as the sun gains in 
elevation, cease to project beyond the shadow of the gentler 
slopes from which it springs. It would be easy to extend this \ 
list of causes of deception ; but those here given may suffice as ’ 
indications of the caution with which it is necessary to approach | 
the much-disputed question of still existing physical change. ! 
In the answer to that question — the affirmative answer — un- I 
doubtedly lies a great part of the charm of selenography. : 
Whatever may be the magnificence of the abrupter features of | 
the lunar scenery, or the smooth and tranquil aspect of its j 
gentler valleys and wide-extended plains, we shall contemplate < 
them with a different amount of interest accordingly as we are | 
obliged to consider them an inanimate and silent record of the 
worn-out and spent convulsions of bygone ages, and forces wholly 
extinct in selenological death ; or whether we may detect if it 
be but the last feeble efforts of that marvellous working which 
