xiv TO TEACHERS AND STUDENTS. 



in those books that treat it best. By reading, you rectify 

 the errors of the ear ; and listening clears up what may 

 have been obscure in reading. If you would clearly under- 

 stand what you hear, read before or after, or both before and 

 after the lecture, what has been published about its subject. 



No one would expect to become a poet or tragedian by 

 simply listening to recitations, or witnessing the representa- 

 tions at a theatre. Nor could any one acquire the infor- 

 mation necessary to be a painter, by simply walking through 

 galleries of pictures. He must resort to books, and study 

 their contents with care and attention. 



In all times, and in all places, all men have felt the ne- 

 cessity of going from spoken to written language. For- 

 merly, pupils drew the lessons of their masters on the 

 leaves of trees, to meditate on them afterwards at leisure. 

 Professors now, very generally, have their respective courses 

 printed, that the student may have the text always at hand 

 for reference and study. 



An individual entering a city for the first time, will make 

 less progress and become less perfectly acquainted with it, 

 if he depend altogether upon his own observation and ver- 

 bal directions, than one who joins to these means of infor- 

 mation, guide-books and maps. To become acquainted 

 with anatomy by merely listening to lectures, or by reading 

 only, or by dissecting alone, unaided either by oral lessons 

 or books, would be the labour of a life-time, even if it be 

 possible at all ; but by joining all these means, by listening 

 to lectures, by reading, and by dissection, he will lessen 

 the labour, abbreviate the time to a few years at most, and 

 attain a perfect and exact knowledge of the science. 



To read, to see, to hear, to study, to observe, and to lis- 

 ten, are not too many means of acquiring solid information 

 of any physical subject. Whoever confines himself to one 

 of these means alone, to the exclusion of all the rest, will 

 never acquire complete knowledge of any physical science. 



