514 Rev. W. V. Harcourt on Lord Brougham's statements 



many educated persons, ignorant of the laws of evidence and 

 unconscious of their own deficiency, become as easy victims as 

 the most ignorant, to wild paradox and blind credulity. 



What the Optics were for experimental philosophy in gene- 

 ral, that little unpretending duodecimo volume, of scarce a 

 hundred pages, which Black published in 1755, on the pro- 

 perties of Magnesia, was to chemistry. It was, as you say, 

 the second instance of a most beautiful example of inductive 

 research; and the method of reasoning pursued in it deserves 

 to be more particularly described, as constituting indeed the 

 highest of all its merits. Not one word is there here of the 

 sulphureous principle of the old chemists, or the correspond- 

 ing phlogistic of the new : but there is, observe, one general 

 established principle, reigning in the experimenter's thoughts, 

 governing his hand, interpreting every phenomenon as it pre- 

 sents itself, dictating every successive experiment, and bring- 

 ing forth each consequent discovery in that brief and trans- 

 parent investigation. 



The principle by which it was thus illuminated, was the 

 principle of elective affinities, — a principle, first stated as we 

 have seen, and generalised by Newton, experimentally noticed 

 by Mayow, with others of the early chemists, and then re- 

 cently systematised and tabulated by the French chemist 

 Geoffroi. And here if we adopt such expressions as yours, 

 in calling this "an example of strict inductive investigation" 

 let us understand clearly what we mean ; let us not forget that 

 the process of what is called the inductive method, in its most 

 usual applications to such a science as chemistry, does not 

 differ from that which is called deductive in mechanics, other- 

 wise than in the degree of our reliance on the generality of 

 the laws to which it is applied : in mechanics we now assume 

 the laws which we have observed, to be applicable to all matter 

 whatever; in chemistry, when the nature of the subject is widely 

 different from those on which we have experimented, we dare 

 not trust the certainty of our generalisations : the firmest be- 

 liever in ajtherial matter would hesitate to presume on New- 

 ton's hypothesis of its possessing chemical affinities, as a cer- 

 tain truth ; and gas was to Black what ccther is to us. His 

 reasonings respecting fixed air were in fact all deductions from 

 the presumed principle of elective attractions; but as far as 

 regards the chief point of his discovery — the silent trans- 

 ference which he remarked of the gaseous substance that, as 

 Hales had taught him, was fixed in salt of tartar, to calcined 

 magnesia, and again from magnesia alba to caustic lime, — the 

 principle which suggested the remark and the experiments, 

 was itself confirmed and established, in its extension to gase- 



