

LECTURE I.] HISTORY OF CHEMISTRY. 3 



that the earlier views, which give expression to a limited num- 

 ber of facts only, must not merely be supplanted by the later 

 theories, which deal with a larger class of phenomena, but that 

 they must lose their importance altogether. For the most part, 

 however, this is not the case. On the contrary, a certain 

 connection between successive hypotheses can very frequently 

 be observed. When the general development is followed up, 

 the effects of the earlier ideas can be recognised in the later 

 views, and it is in this way that the latter first come to be 

 properly understood. The abandonment of a theory is not 

 always accompanied by a revolution. Such, indeed, is scarcely 

 conceivable in the higher stages of the development of science ; 

 and even when new modes of explanation are proposed, traces 

 of former opinions may still be recognised in the direction which 

 these take. 



But quite apart from this real advantage of the study of 

 history, which thus, in my opinion, leads to a clearer under- 

 standing of our present position, yet another advantage may 

 be adduced which is perhaps of still greater value to the 

 student : namely, the accurate estimation of the value of 

 theories. An examination of the past shows us the muta- 

 bility of opinions ; it enables us to recognise how hypotheses, 

 apparently the most securely established, must in course of 

 time be abandoned. It leads us to the conviction that we 

 live in a state of continuous transition ; that our ideas of to- 

 day are merely the precursors of others ; and that even they 

 cannot, for any length of time, satisfy the requirements of 

 science. We learn from any historical exposition that our 

 natural laws are not incontrovertible truths or revelations, 

 but that they can be regarded as the expression, for the time 

 being, of a certain series of facts, which are thereby summarised 

 and, as we say, explained in the most practical way for us. 

 We recognise that these laws do not originate suddenly in the 

 head of a single individual, like Minerva in the head of Jupiter. 

 It is only slowly that the fundamental ideas which underlie 

 them mature, and that the requisite facts are ascertained by the 

 labours of many ; until, at last, the law common to them all is 



