THIRD AMERICAN EDITION. XI 



world, enhanced by the practical and useful ends to 

 which he has turned his discoveries." 



To Dr. S. L. Dana, of Lowell, the editor would ac- 

 knowledge his obligations for valuable suggestions 

 and the communication of some important additions, 

 and also to Mr. Charles E. Buckingham, of the Medical 

 School of this University, for his valuable assistance 

 in correcting the proofs. 



J. W. W. 



Cambridge, September, 1842. 



