In a similar way it may be assumed that atmospheric gases can be given off from the crust of the moon, thus, to a greater or less extent, supplying the place of the molecules that escape.] After it had been found that, to ordinary tests, the moon offered no evidence of the possession of an atmosphere, and before Dr.Stoney's theory was broached, it was supposed by many that the moon had lost its original supply of air by absorption into its interior.

The oxygen was supposed to have entered into combination with the cooling rocks and minerals, thus being withdrawn from the atmosphere, and the nitrogen was imagined to have disappeared also within the lunar crust.

For it seems to have always been tacitly assumed that the phenomenon to be accounted for was not so much the _absence_ of a lunar atmosphere as its _disappearance_.

But disappearance, of course, implies previous existence.

In like manner it has always been a commonly accepted view that the moon probably once had enough water to form lakes and seas.
These, it has been calculated, could have been absorbed into the lunar globe as it cooled off.