232 THR EARTH'S INTERIOR. 



rigid, cooling body, with a crust occasionally col- 

 lapsing upon the shrinking centre, but on the whole 

 progressively more hard as we move from the 

 the known and knowable outside toward the un- 

 known core. And, whether this conception be 

 wholly and fully correct or otherwise, it is at least 

 some consolation to reflect that we shall never in 

 all probability get any experimental proof to the 

 contrary. That is the best of all such cosmical 

 speculations ; if you are wrong, you have, at any 

 rate, the comfort of feeling that nobody else can 

 be much wiser. Volcanoes and earthquakes may 

 help us to arrive gradually at fuller conceptions 

 upon this abstruse point. The constant observa- 

 tion of Vesuvius and Etna, the examination of 

 extinct ancient craters, and even the result of 

 spectroscopic analysis in other stars, may also as-* 

 sist us in coming hereafter to a final conclusion. 

 But, on the whole, it is at least probable that we 

 shall never know, with absolute certainty, the 

 exact constitution of the earth's centre. And yet 

 " never " is a long word. Now that we are begin- 

 ning to analyze the sun, and to determine the 

 component elements of the distant haze-clouds, it 

 is not perhaps too much to expect that we may 

 some day decide the difficult problem of the earth's 

 interior. 



