452 Notices of Memoirs — Professor Sottas' s Address 



1 



of iron. Lord Kelvin has admitted the probable existence of some 

 such nucleus, and lately Professor Wiechert has furnished us with 

 arguments — "powerful" arguments Professor Darwin terms them — 



in support of its existence 



The outer envelope of the earth which was drawn off to form the 

 moon was, as we have seen, charged with steam and other gases 

 under a pressure of 5,000 lb. to the square inch ; but as the satellite 

 wandered away from the parent planet this pressure continuously 

 diminished. Under these circumstances the moon would become 

 as explosive aa a charged bomb, steam would burst forth from 

 numberless volcanoes, and while the face of the moon might 

 thus have acquired its existing features the ejected material might 

 possibly have been shot so far away from its origin as to have 

 acquired an independent orbit. If so, we may ask whether it may 

 not be possible that the meteorites, which sometimes descend upon 

 our planet, are but portions of its own envelope returning to it. 

 The facts that the average specific gravity of those meteorites which 

 have been seen to fall is not much above 3-2, and that they have 

 passed through a state of fusion, are consistent with this suggestion. 



Second Critical Period : " Consistentior Status." 

 The solidification of the earth probably became completed soon 

 after the birth of the moon. The temperature of its surface at the 

 time of consolidation was about 1170° C., and it was therefore still 

 surrounded by its primitive deep atmosphere of steam and other 

 gases. This was the second critical period in the history of the 

 earth, the stage of the " consistentior status," the date of which 

 Lord Kelvin would rather know than that of the Norman Conquest, 

 though he thinks it lies between twenty and forty millions of years 

 ago, probably nearer twenty than forty. 



Now that the crust was solid there was less reason why move- 

 ments of the atmosphere should be unsteady, and definite regions of 

 high and low pressure might have been established. Under the 

 high-pressure areas the surface of the crust would be depressed ; 

 correspondingly, under the low-pressure areas it would be raised ; 

 and thus from the first the surface of the solid earth might be 

 dimpled and embossed. 



Third Critical Period: Origin of the Oceans. 



The cooling of the earth would continuously progress, till the 

 temperature of the surface fell to 370° C, when that part of the 

 atmosphere which consisted of steam would begin to liquefy ; then 

 the dimples on the surface would soon become filled with super- 

 heated water, and the pools so formed would expand and deepen till 

 they formed the oceans. This is the third critical stage in the 

 history of the earth, dating, according to Professor Joly, from 

 between eighty and ninety millions of years ago. With the growth 

 of the oceans the distinction between land and sea arose — in what 

 precise manner we may proceed to inquire 



The ocean when first formed would consist of highly heated 

 water, and this, as is well known, is an energetic chemical reagent 



