ERRATA. 



Insert " as observed " before " at Castle William," sixth line from the bottom 

 of page 259. 



Instead of a dash before " potash," page 271, eighth line from the bottom of the 

 page, substitute a comma after that word. 



Substitute a period for the note of admiration on page 285, twelfth line. 



The experiment exhibited by Mr. Guyot, and described on page 284, where it 

 is credited to Professor Snell, is identical with that performed by M. de Maistre 

 in 1832, of which an account is given in Peltier's work, " Des Trombes," 

 page 11. 



