THE DOCTRINE OF NATURAL SELECTION. 27 



probability, at some more distant epoch, on other grounds. The great 

 depths of the oceans extend over wide areas, whereas the great heights 

 of the land are only narrow ridges and peaks ; hence it has been cal- 

 culated that the mean height of the land is only 1,000, while the mean 

 depth of the sea is about 15,000 feet. But the sea is 2| times as ex- 

 tensive as the land, so that the bulk or mass of the land above the sea- 

 level will be only about one thirty-seventh of the mass of the ocean. 

 Now, does not this small proportion of bulk of land to water render it 

 highly probable that the forces of elevation and depression should 

 sometimes cause the total or almost total submersion of the land ? 

 Of such an epoch no geological record could be left because there 

 could be no strata formed, except from the debris of coral-islands, and 

 such a period of destruction of the greater part of terrestrial life may 

 have repeatedly occurred between the period when the several Primary 

 or Secondary formations were deposited. At all events, with such a 

 proportion of land and sea surface as now exists, with such a small 

 bulk of land above the enormous bulk of water, and with no known 

 cause why the dry land rather than the sea-bottom should be con- 

 stantly elevated, we must admit it to be almost certain that great fluc- 

 tuations of the area of the land must occur, and that, while those fluc- 

 tuations could not very considerably increase the area of the land they 

 might immensely diminish it. There is here, therefore, a cause for 

 the possible depopulation of the earth likely to occur much sooner 

 than any cosmical catastrophe. 



The largest and most elaborate essay in the volume is that on the 

 " History of the Sciences and of Scientific Men for the last Two Cen- 

 turies." In this the author endeavors to arrive at certain conclusions 

 as to the progress of science under different conditions and in different 

 countries, the influence of political institutions and of heredity, and 

 various other phenomena, by a method which is novel and ingenious. 

 He takes account only of the men honored as foreign associates or 

 members by the three great European scientific bodies, the Royal So- 

 ciety of London and the Paris and Berlin Academies. By this means 

 he avoids all personal bias, and secures, on the whole, impartiality. 

 The tables drawn out by this method are examined in every possible 

 way, and the results worked out in the greatest detail. The main con- 

 clusion arrived at is the determination of a series of eighteen causes 

 favorable to the progress of science ; and it is shown that a large 

 proportion of these are present in a considerable degree in coun- 

 tries where science flourishes, while they are almost wholly absent 

 in barbarous or semi-civilized countries where science does not 

 exist. 



Another interesting essay is that on the importance for science of a 

 dominant language, and it contains some very curious facts as to the 

 way in which the English language is spreading on the Continent. M. 

 de Candolle believes that in less than two centuries English will be 



