Reverting to the consequences of the terrestrial atmosphere: one of the most striking of these is the phenomenon of diffused daylight, which we need hardly remind the reader is produced by the scattering or diffusion of the sun’s rays among the minute particles of vapour composing or contained in that atmosphere. Were it not for this reflexion and diffusion of the sun’s light, those parts of our earth not exposed to direct sunshine would be hidden in darkness, receiving no illumination beyond the feeble amount that might be reflected from proximate terrestrial objects actually illuminated by direct sunlight. Twilight is a consequence of this reflexion of light by the atmosphere when the sun is below the horizon. If, then, an atmosphere enveloped the moon, we should see by diffused light those parts of the lunar details that are not receiving the direct solar beams; and before the sun rose and after it had set upon any region of the moon, that region would still be partially illuminated by a twilight. But, on the contrary, the shadowed portions of a lunar landscape are pitchy black, without a trace of diffused-light illumination, and the effects that a twilight would produce are entirely absent from the moon. Once, indeed, one observer, Schroeter, noticed something which he suspected was due to an effect of this kind: when the moon exhibited itself as a very slender crescent, he discovered a faint crepuscular light, extending from each of the cusps along the circumference of the unenlightened part of the disc, and he inferred from estimates of the length and breadth of the line of light that there was an atmosphere about the moon of 5376 feet in height. This is the only instance on record, we believe, of such an appearance being seen. [Illustration: Fig. 12.]