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.