PRESIDENTIAL ADDRESS, B.A. 1871. 187 



Leverrier's researches on the motion of the planet 

 Mercury, though giving evidence of a sensible 

 influence attributable to matter circulating as a 

 great number of small planets within his orbit 

 round the Sun, showed that the amount of matter 

 that could possibly be assumed to circulate at any 

 considerable distance from the Sun must be very 

 small ; and therefore, " if the meteoric influx 

 " taking place at present is enough to produce any 

 " appreciable portion of the heat radiated away, it 

 " must be supposed to be from matter circulating 

 <( round the Sun, within very short distances of 

 " his surface. The density of this meteoric cloud 

 " would have to be supposed so great that comets 

 " could scarcely have escaped, as comets actu- 

 " ally have escaped, showing no discoverable 

 " effects of resistance, after passing his sur- 

 " face within a distance equal to one-eighth of 

 "his radius. All things considered,' there seems 

 " little probability in the hypothesis that solar 

 " radiation is compensated to any appreciable 

 " degree by heat generated by meteors falling in, 

 " at present ; and, as it can be shown that no 



