iSS POPULAR LECTURES AND ADDRESSES. 



" chemical theory is tenable, 1 it must be concluded 

 " as most probable that the Sun is at present 

 " merely an incandescent liquid mass cooling." '- 



Thus on purely astronomical grounds was I long 

 ago led to abandon as very improbable the 

 hypothesis that the Sun's heat is supplied dynami- 

 cally from year to year by the influx of meteors. 

 Hut now spectrum analysis gives proof finally 

 conclusive against it. 



Each meteor circulating round the Sun must 

 fall in along a very gradual spiral path, and before 

 reaching the Sun must have been for a long time 

 exposed to an enormous heating effect from his 

 radiation when very near, and must thus have been 

 driven into vapour before actually falling into the 

 Sun. Thus, if Mayer's hypothesis is correct fric- 

 tion between vortices of meteoric vapours and the 

 Sun's atmosphere must be the immediate cause of 

 solar heat ; and the velocity with which these 

 vapours circulate round equatorial parts of the 

 Sun must amount to 435 kilometres per second. 



1 " Mechanical Kneri^ies," \v. 



- " A|;c of the Sun's I leal " (Muc/ni/la/i s .l/<^;///<', March, 1862). 



