MIRACLES OF SCIENCE 



Neptune, were pretty generally supposed to be not 

 unlikely abodes for human beings by astronomers 

 even of half a century ago. But we have just seen 

 that the recent tests prove that those great bodies 

 have far too tenuous a structure to be other than 

 gaseous in constitution; at the very most their cen- 

 tral portions may have the structure of molten 

 liquids. Jupiter's equatorial portions are observed 

 to rotate more rapidly than parts nearer the poles, 

 thus proving by direct observation the condition of 

 fluidity argued by the mathematicians. In a word, 

 then, these gigantic planets are worlds in the making. 

 By no possibility can they at present give habitation 

 to living creatures in any wise comparable to those 

 that inhabit the earth. 



For a quite different reason the tiny interior planet 

 Mercury is uninhabitable. It is all but certain that 

 this planet has been brought by tidal strain to a con- 

 dition comparable to that of our moon in which its 

 period of rotation corresponds exactly to its period 

 of revolution, so that it turns one face always to the 

 sun just as the moon always turns one face to the 

 earth. The result must be that one half the surface 

 of Mercury is intolerably hot and the other half in- 

 tolerably cold as well as perpetually dark. 



Overlooking the company of tiny asteroids, there 

 remain two planets, Mars and Venus. These 'are 

 nearest neighbors, and they rather closely resemble 

 the earth in size and density of structure. They are 

 both of such constitution as to give the idea of their 

 habitability greater or less plausibility; and that 

 Mars is in reality inhabited has become almost a 



86 



