228 THE BORDERLAND OF SCIENCE. 



would theoretically reduce the moon's distance to one 

 hundred miles, the atmosphere between us and the 

 moon is, as it were, multiplied 2,400 times. 



But we have not even yet exhausted all the ingenious 

 theories which have been devised by those who insist 

 on endowing the moon of former ages with oceans and 

 an atmosphere. We have seen a comet called in to 

 carry away the lunar air and water ; next we have had 

 them frozen up ; and thirdly, the moon's interior has 

 opened to remove them from our sight. But a fourth 

 theory remains, which, though not less startling than 

 the others, has found singular favour even among 

 astronomers of repute. According to this fourth 

 theory, the lunar oceans and atmosphere have with- 

 drawn, not into the inside of the moon, but to her 

 other or unseen side. The farther half of the moon is 

 never seen by us, and being unknown has appeared 

 to afford a favourable opportunity of applying the 

 principle 'ornne ignotum pro mirifico.' Accordingly^ 

 it has been supplied with oceans and an atmosphere, 

 in fact with a double quantity of air and water; 

 inhabitants are, of course, not wanting where circum- 

 stances are so suitable for their subsistence ; and in 

 fine, another world exists on the unseen half of the 

 moon. 



It would be unfair, however, to describe this theory 

 as though it were merely based on our ignorance of the 

 state of things on the farther side of the moon, as 

 though, in fact, it resembled one of the peut-etres of 

 Fontenelle (who was an ardent believer, by the way, 



