208 Dr. Henry on t?ie Philosophical Character of Dr. Priestley. 



history of that department of science, which Dr. Priestley cul- 

 tivated with such extraordinary success ; and still more, for 

 estimating the value of his discoveries, and adjusting his station 

 as an experimental philosopher, — the simple narrative, which 

 he originally gave in the order of time, supplies the amplest 

 and the firmest ground-work. 



In everything that respects the history of this branch of 

 experimental philosophy, the writings and researches of Dr. 

 Priestley, to which I have alluded, are peculiarly instructive. 

 They are distinguished by great merits, and by great defects ; 

 the latter of which are wholly undisguised by their author. 

 He unveils with perfect frankness the whole process of reason- 

 ing, which led to his discoveries; he pretends to no more 

 sagacity than belonged to him, and sometimes disclaims even 

 that to which he was fairly entitled ; he freely acknowledges 

 his mistakes, and candidly confesses when his success was the 

 result of accident, rather than of judicious anticipation ; and 

 by writing historically and analytically, he exhibits the pro- 

 gressive improvement of his views, from their first dawnings 

 to their final and distinct development. Now, with whatever 

 delight we may contemplate a systematic arrangement, the 

 materials of which have been judiciously selected, and from 

 which everything has been excluded that is not essential to the 

 harm()n3'of the general design, yet there can be no question that 

 as elucidating the operations of the human mind, and enabling 

 us to trace and appreciate its powers of invention and discovery, 

 the analytic method of writing has decided advantages. 



To estimate justly the extent of Dr. Priestley's claim to 

 philosophical reputation, it is necessary to take into account 

 the state of our knowledge of gaseous chemistry at the time 

 when he began his inquiries. Without underrating what had 

 been already done by Van Helmont, Ray, Hooke, Mayow, 

 Boyle, Hales, Macbride, Black, Cavendish, and some others, 

 Priestley may be safely affirmed to have entered upon a field, 

 which, though not altogether untilled, had yet been very 

 imperfectly prepared to yield the rich harvest which he 

 afterwards gathered from it. The very implements with 

 which he was to work were for the most part to be invented ; 

 and of the merits of those which he did in /cut, it is a suffi- 

 cient proof that they continue in use to this day, with no very 

 important modifications. All his contrivances for collecting, 

 transferring, and preservingdiffijrent kinds of air, and for sub- 

 mitting those airs to the action of solid and liquid substances, 

 were exceedingly simple, beautiful, and effectual. They were 

 chiefly, too, the work of his own hands, or were constructed 

 under his directions by unskilled persons ; for the class of in- 

 genious 



