222 THE BORDERLAND OF SCIENCE. 



the dead globe we see, never to be warmed again into 

 life, and having no other use in the economy of the 

 universe but to illuminate our earth and regulate her 

 tides. 



But while it is quite conceivable that the intensity 

 t>f cold during the long lunar nights may be amply 

 sufficient to turn every gas we know of into the solid 

 form, it is manifest that the intense heat to which the 

 moon is exposed during her equally long day would 

 produce even more remarkable changes when poured 

 upon such a frozen surface than it would effect on such 

 a globe as our earth in its present condition. Imagine 

 our oceans frozen, and the air also frozen, so as to lie 

 in great drifts many feet deep* over the whole surface 

 of the globe. Then conceive the sun to pour his rays 

 down upon that frozen surface for a day lasting two of 

 our weeks, his midday place being nearly overhead. Is 

 it not manifest that the frozen air would be melted and 

 vaporised (turned, that is, into our familiar air) and 

 then the ocean melted, and enormous quantities turned 

 into vapour. Such are the actual conditions in those 

 lunar regions which form the middle of the moon's 

 face. Yet at the time of full moon no signs of change 

 can be recognised, at least none which correspond to 



* We do not know the actual depth, because we do not know what is 

 the density of solid oxygen or solid nitrogen. But we know that if the 

 density of these elements, when reduced to the solid state, were equal to 

 that of ice, the atmosphere would be converted into a solid layer, more 

 than thirty feet deep, for the water-barometer stands at more than thirty 

 feet. If frozen oxygen and nitrogen are as dense as mercury, then the 

 layer would be only two and a half feet in depth. 



