112 LAY SERMONS, ADDRESSES, AND REVIEWS. [yi. 



Seeking for the cause of this difference, I imagine I 

 can find it in the fact, that, in the world of letters, 

 learning and knowledge are one, and books are the 

 source of both ; whereas in science, as in life, learning 

 and knowledge are distinct, and the study of things, 

 and not of books, is the source of the latter. 



All that literature has to bestow may be obtained 

 by reading and by practical exercise in writing and 

 in speaking ; but I do not exaggerate when I say, that 

 none of the best gifts of science are to be won by these 

 means. On the contrary, the great benefit which a 

 scientific education bestows, whether as training or as 

 knowledge, is dependent upon the extent to which the 

 mind of the student is brought into immediate contact 

 with facts — upon the degree to which he learns the 

 habit of appealing directly to Nature, and of acquiring 

 through his senses concrete images of those properties 

 of things, which are, and always will be, but approxi- 

 matively expressed in human language. Our way of 

 looking at Nature, and of speaking about her, varies 

 from year to year ; but a fact once seen, a relation of 

 cause and effect, once demonstratively apprehended, are 

 possessions which neither change nor pass away, but, 

 on the contrary, form fixed centres, about which other 

 truths aggregate by natural affinity. 



Therefore, the great business of the scientific teacher 

 is, to imprint the fundamental, irrefragable facts of his 

 science, not only by words upon the mind, but by 

 sensible impressions upon the eye, and ear, and touch 

 of the student, in so complete a manner, that every 

 term used, or law enunciated, should afterwards call 

 up vivid images of the particular structural, or other, 

 facts which furnished the demonstration of the law, or 

 the illustration of the term. 



Now this important operation can only be achieved 



