TRANSACTIONS. 
G1 
in octavo, which were published by him, at intervals between 
the years 1774 and 1786; the first three under the title of 
“ Experiments and Observations on different kinds of Air; ” 
and the last three under that of “ Experiments and Observa¬ 
tions relating to various Branches of Natural Philosophy, with 
a continuation of the Observations on Air.” These volumes 
were afterwards methodized by himself, and compressed into 
three octavos, which were printed in 1790. As a record of 
facts, and as a book of reference, the systematized work is to be 
preferred. But as affording materials for the history of that 
department of science, which Dr. Priestley cultivated 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 reasoning, 
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 mis¬ 
takes, 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 progressive 
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 every¬ 
thing has been excluded, that is not essential to the harmony 
of the general design, yet there can be no question that as elu¬ 
cidating 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 Plelmont, 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 im- 
