viii PREPACK TO SECOND EDITION 



supposes him to have already read soim su< h text-book ; 

 to have acquired a general knowledge of the scope of 

 the science; and to have become, in some 

 f.imili.ir with the facts. Its purpose is to be sugp 

 to him, rather than didactic ; to put him in the way of 

 intelligently observing for himself, rather than to pi 

 him witli what has already been discovered by others. 



COLLEGE, LI>:M 

 February J&JQ. 



