of Edinburgh, Session 1882-83. 
187 
Monday, 21st May 1883. 
Mr EGBERT GRAY, Vice-President, in the Chair. 
The Chairman read Communications from the Science and Art 
Department, and from the Education Department. 
The Chairman read Obituary Votices of Sheriff Frederick Hallard, 
Dr John Muir, Friedrich Wohler, and Sir John Rose Cormack, 
deceased Fellows of the Society. 
The following Communications were read : — 
1. On the Moon and the Weather. By John Aitken. 
When residing in the south of France lately, I happened to look 
at the new moon one evening through the clear air of the “Mistral,” 
which was blowing at the time, and not being able to see the dark 
body of the moon, it all at once struck me that something more was 
necessary than a clear atmosphere in order to enable us to see the 
dark side of the moon, and that the dark side would be best seen 
when the earth was to a great extent covered with clouds. 
When we look at the moon when it is a few days old we see that 
the part of it turned towards the sun is brilliantly illuminated, and 
that the part in shadow is dark. Further, the degree of illumination 
of the dark part is known to vary, and is generally supposed to be 
brightest when our atmosphere is clearest. 
Now it is evident that while the sun can illuminate the side of 
the moon turned towards it, it is quite unable to throw any light on 
the parts in shadow, as there is no atmosphere or anything round the 
moon to reflect the light to the shadows. The result is, that so far 
as the direct rays of the sun are concerned, the dark side of the 
moon would be quite invisible to us. 
If we now transport ourselves in imagination to any part of the 
moon’s surface that is in shadow, we would see our earth like a large 
moon, which would wax and wane exactly as the moon appears to 
us, only in the reverse order. When we have no moon on the earth, 
the earth will appear fully illuminated from the moon ; and when 
we have full moon, the earth will shed no light ou the moon. In 
