4 Physical Changes upon the Moon's Surface . [January, 
surfac2. Approaching the study of the moon with strongly 
preconceived notions that the surface is a mere arid 
desert, nearly red-hot at times and almost immeasurably 
cold at others, without water, air, or life, the real condition 
of the moon is not such as to dissipate these views at the 
first glance. Its cold, still, apparently unchangeable sur- 
face, so utterly unlike what the earth might be supposed to 
appear as seen from the moon, convinces the casual observer 
that the world he then sees is utterly unlike the world he 
knows. He looks for immense cloud-masses floating in a 
dense atmosphere, and sees none ; for wave-tossed seas and 
winding broad rivers, and there are none ; searches for lux- 
uriant forests and green prairies, and they are absent. This 
is enough, and he retires from further contemplation of the 
“ airless, waterless, lifeless, volcanic desert ” of the text- 
books. During subsequent periods he may again take a 
casual glance of our satellite, look at lunar occultations, 
or watch the grand changes in appearance that the face of 
the moon presents as the sun sweeps across its heavens and 
slowly illuminates: in turn its varied formations. But study 
the surface, endeavour to piece together bit by bit the dif- 
ferent features that are revealed, until he thoroughly com- 
prehends the details and nature of the formations he sees, 
is what the general observer and the great majority of 
astronomers do not even attempt to do.* To properly 
become acquainted with the nature of the lunar surface 
requires that the study of the moon should be made the 
primary objeCl of one’s observations; and those who have 
done this, and devoted years to the assiduous study of the 
moon, constitute those astronomers who — as previously 
mentioned — hold different views as to the present condition 
of the lunar surface to astronomers in general. 
The previous observations are, it will be seen, of im- 
portance in connection with the subject of the present 
article, for they show how selenographers and astronomers 
in general may hold very different opinions on questions 
connected with the moon, — one are led to conclusions from 
the careful study of the minuter details of the lunar forma- 
* An interesting instance, illustrating the condition of the general knowledge 
of selenographical subjects amongst astronomers, is the prevailing opinion 
that no retardation of occultation of stars by the moon has ever been observed, 
but that stars approach the limb of the moon, and disappear behind it at the 
instant they theoretically should. Yet it has been stated repeatedly that the 
only three series of redu&ions of the observation of occultation of stars show 
that a very considerable retardation does take place — a retardation of from 
5 to io, and often even 15 seconds of time. Different opinions maybe held as 
to the cause of this retardation of occultation, but of the faCt there can be no 
question, and it has been known for nearly twelve years. 
