THE LUNAR WORLD. 85 



both the presence of air and the presence of water ; we 

 do not of course say that in other parts of the universe 

 there may not be types of life for which neither air nor 

 water is essential ; nothing is, however, more clear than 

 the evidence which we are able to produce with reference 

 to the presence on, or absence from, the moon, of the sub- 

 stances we have named. First, with regard to water. I 

 have already had occasion incidentally to allude to this 

 subject; there are, no doubt, some reasons for thinking 

 that there may have been at one time water on the moon, 

 but it is now certain that there is no liquid on its surface, 

 nor indeed can I find much reason to believe that there is 

 even frozen water there, as has been sometimes supposed. 

 It is certainly a singular fact that two constituents which 

 are so abundant here should seem to be entirely wanting 

 in the moon, and it is an interesting speculation to con- 

 sider what has happened to the water on the moon if it 

 once existed there. 



It is generally believed that as our satellite cooled down 

 the water penetrated into the interior, and was there 

 seized upon by the minerals which required water in 

 order that they might assume their appropriate crystalline 

 forms. The water on the moon has therefore, accord- 

 ing to this view, become transformed into a solid and 

 incorporated with the bodily texture of the globe. It 

 has even been surmised that a similar destiny awaits the 

 oceans on our own globe ; broad and deep though they 

 are, they yet may be inadequate to quench the thirst for 

 water possessed by so vast a mass of crystallizing mine- 

 rals as must exist in the interior of the globe. But 

 whether this be the explanation of the absence of liquid 



