But as every additional glass is an additional obstruction to the light, the object glass of a Lunar telescope is employed without a corrector; light is thereby saved, and in viewing the Moon, as in viewing a map, it evidently makes very little difference whether we see her inverted or not.

Maps of the Moon therefore, being drawn from the image formed by the telescope, show the north in the lower part, and _vice versa_.

Of this kind was the _Mappa Selenographica_, by Beer and Maedler, so often previously alluded to and now carefully consulted by Barbican.

The northern hemisphere, towards which they were now rapidly approaching, presented a strong contrast with the southern, by its vast plains and great depressions, checkered here and there by very remarkable isolated mountains.[A] At midnight the Moon was full.

This was the precise moment at which the travellers would have landed had not that unlucky bolide drawn them off the track.