PRESIDENTIAL ADDRESS, B.A. 1871. 201 



or explicitly, all men discard it. It is often 

 assumed that all, and it is certain that some, 

 meteoric stones are fragments which had been 

 broken off from greater masses and launched free 

 into space. It is as sure that collisions must occur 

 between great masses moving through space as it 

 is that ships, steered without intelligence directed 

 to prevent collision, could not cross and recross the 

 Atlantic for thousands of years with immunity 

 from collisions. When two great masses come into 

 collision in space it is certain that a large part of 

 each is melted ; but it seems also quite certain that 

 in many cases a large quantity of debris must be 

 shot forth in all directions, much of which may 

 have experienced no greater violence than in- 

 dividual pieces of rock experience in a land-slip 

 or in blasting by gunpowder. Should the time 

 when this Earth comes into collision with another 

 body, comparable in dimensions to itself, be when 

 it is still clothed as at present with vegeta- 

 tion, many great and small fragments carrying 

 seed and living plants and animals would un- 

 doubtedly be scattered through space. Hence and 



