12 PRESIDENTIAL ADDRESS. 
eccentricity until, in time, a regular system would be de- 
veloped, when the whole of the meteorites would travel 
nearly in the mean plane of their aggregate motions. The 
larger of the meteorites would tend to settle towards the 
centre, while other aggregations might easily occur at dif- 
ferent distances from the centre. And of these, the outer 
planets would be larger than the inner ones, because, in the 
more distant regions, where the attraction of the central sun 
was less, the movements of the meteorites would be slower, 
and there would be a greater tendency to agglomeration 
than where the movements were more rapid. As meteorites 
contain but little oxygen, hydrogen, carbon, silicon, and 
alkalies—substances which are all abundant on the surface 
of the earth—large numbers must have been fused together 
to form the earth, and the lighter substances must have col- 
lected near the surface. Consequently, the collisions be- 
tween these meteorites must have occurred with sufficient 
rapidity to melt the whole mass. For, after a solid crust 
had been formed, all the meteorites which fell on the earth 
would remain on the surface, as they do now. 
As with the Solar System, so, also, in the earth itself we 
can trace distinctly a physical evolution. The discovery of 
tidal friction gave an independent proof that the earth had 
had a beginning not infinitely remote, for, if that had been 
the case, the tidal friction would have reduced the time of 
the earth’s rotation on its axis to that of the moon. Also, 
’ we have sufficient geological evidence to show that not more 
than one hundred millions of years ago the earth was in a 
molten condition, and, probably, shone with its own light. 
As cooling went on, the silicates crystallised out, forming a 
solid crust over the still molten, metallic interior, and the 
earth then became a dark body. At that time, all the 
water above the crust was in a state of vapour, which, sub- 
sequently, fell as hot rain, forming a boiling ocean. With 
this rain the denudation of the primitive crystalline rocks 
commenced, and their débris was deposited on the bed of 
the ocean as sedimentary rocks. Gradually, the continents 
were formed, the new ranges of mountains following each 
other in orderly succession, the great oceans becoming nar- 
rower and deeper, as well as more and more salt. These 
processes are still going on, but, as the earth is cooling, the 
internal energy which uplifts the mountains must be dimin- 
ishing, and, in time, it will be insufficient to counteract the 
denudation. Then the whole of the land will be swept into 
the sea, and the waves of the ocean will roll over the surface 
of the earth unopposed. Unless, indeed, before that time 
arrives, the ocean should have been frozen into a mass of ice, 
cae 
