TRANSACTIONS. 
65 
than were then known; from the properties of which, and from 
those of their combinations, tentative approximations to general 
principles might at first be deduced; to be confirmed or cor¬ 
rected, enlarged or circumscribed, by future experience. It 
would have retarded the progress of science, and put off, to a 
far distant day, that affluence of new facts, which Priestley so 
rapidly accumulated, if he had stopped to investigate, with 
painful and rigid precision, all the minute circumstances of 
temperature, of specific gravity, of absolute and relative weights, 
and of crystalline structure, on which the more exact science of 
our own times is firmly based, and from which its evidences 
must henceforward be derived. Nor could such refined inves¬ 
tigations have then been carried on with any success, on account 
of the imperfection of philosophical instruments. It would have 
been fruitless, also, at that time, to have indulged in specula¬ 
tions respecting the ultimate constitution of bodies ;—specula¬ 
tions that have no solid ground-work, except in a class of facts 
developed within the last thirty-five years, all tending to esta¬ 
blish the laws of combination in definite and in multiple propor¬ 
tions, and to support the still more extensive generalization, 
which has been reared by the genius of Dalton. 
It was, indeed, by the activity of his intellectual faculties, 
rather than by their reach or vigour, that Dr. Priestley was 
enabled to render such important services to natural science. 
We should look, in vain, in any thing that he has achieved, for 
demonstrations of that powerful and sustained attention, which 
enables the mind to institute close and accurate comparisons ;—- 
to trace resemblances that are far from obvious;—and to dis¬ 
criminate differences that are recondite and obscure. The 
analogies, which caught his observation, lay near the surface, 
and were eagerly and hastily pursued; often, indeed, beyond 
the boundaries, within which they ought to have been circum¬ 
scribed. Quick as his mind was in the perception of resem¬ 
blances, it appears (probably for that reason,) to have been little 
adapted for those profound and cautious abstractions, which 
supply the only solid foundations of general laws. In sober, 
patient, and successful induction, Priestley must yield the palm 
to many others, who, though far less fertile than himself in new 
and happy combinations of thought, surpassed him in the use 
of a searching and rigorous logic ; in the art of advancing, by 
secure steps, from phenomena to general conclusions ;—and 
again in the employment of general axioms as the instruments 
of further discoveries. 
Among the defects of his philosophical habits, may be re¬ 
marked, that he frequently pursued an object of inquiry too 
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