186 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
ground—that is, what manner of landscape would greet his wonder- 
ing eye. 
The very accurate data which astronomers possess as to the struc- 
ture of the lunar terrain greatly facilitates this problem. For 
geometry enables us to put easily into actual perspective all the 
details which the telescope allows us to see in relief under an oblique 
illumination. Remember, in passing, that the shadows are sharply 
delineated and that they may be seen to elongate as the sun rises 
or sets for different regions of the lunar surface. This enables ‘us 
to calculate exactly the heights of the various parts of this surface. 
It is astonishing, despite these exact data, what phantastic repre- 
sentations have been drawn of the landscapes of this lunar world. 
Numerous astronomical treatises have represented them as embel- 
lished with mountains and peaks made of jagged sugar loafs, at the 
feet of which are heaped numerous small vatlike formations having 
the appearance of volcanic molehills. Actually the lunar mountains 
have profiles comparable in their steepness to our own terrestrial 
mountains. The great majority of the circular formations are of such 
size that we would be unable to see their whole extent in a single 
glance. It would be necessary to turn around in order to see their cir- 
cular walls which would appear like a long chain of more or less irreg- 
ular mountains. For some of them, if we were at their center, their 
ramparts would be so far distant as to be invisible, lost below our 
horizon. We must further remember that on the moon, because of 
the greater curvature of its globe, relative to the stature of man, 
the horizon is closer, and therefore objects disappear behind it at 
a shorter range. Only those craters which are very small and 
numerous and whose diameters are of the order of a kilometer may 
be wholly seen from one place. We should in no way compare them 
with the ordinary volcano whose crater is a cavity at the top of an 
elevated cone. The lunar craters, despite this name with which they 
are often designated, are comparable to excavations whose bottom 
levels are very much below the surrounding lunar surface above 
which the exterior surrounding walls rise very little. 
As to the extended gray plains, erroneously called seas, their great 
smooth surfaces must present a remarkably monotonous aspect 
broken here and there by immense fissures whose gigantic propor- 
tions have no parallel upon our earth. 
We can reproduce the contour of any given region on the moon 
since we have comparatively precise measures. Though such views 
can not lay claim to an absolute fidelity, they are probably nearly 
true. They contain a certain dose of imagination indispensable to 
fill the gaps in our knowledge of the minuter details. They, how- 
ever, can show us in an expressive fashion the general character of 
these extra-terrestrial regions. 
