Dr. Henry on the Philosophical Character of Dr. Priestley. 211 



solved to multiply experiments, with the view of increasing 

 the numerical probabilities of discovery. We find him con- 

 fessing, on one occasion, that he " was led on by a random 

 expectation of some change or other taking place." In other 

 instances, he was influenced by theoretical views of so flimsy 

 a texture, that they were dispersed by the first appeal to ex- 

 periment. "These mistakes," he observes, "it was in my 

 power to have concealed ; but 1 was determined to show how 

 little mystery there is in the business of experimental philo- 

 sophy ; and with how little sagacity discoveries, which some 

 persons are pleased to consider great and wonderful, have been 

 made." Candid acknowledgements of this kind were, however, 

 turned against him by persons envious of his growing fame ; 

 and it was asserted that all his discoveries, when not the huits of 

 plagiarism, were "lucky guesses," or owing to mere chance *. 

 Such detractors, however, could not have been aware of the 

 great amount of credit that is due to the philosopher, who at 

 once perceives the value of a casual observation, or of an un- 

 expected result ; who discriminates what facts are trivial, and 

 what are important; and selects the latter to guide him through 

 difficult and perplexed mazes of investigation. In the words 

 of D'Alembert, " Ces hazards ne sont que pour ceux qui jouent 

 Men:' 



The talents and qualifications which are here represented 

 as having characterized the mind of Dr. Priestley, though not 

 of the rarest kind, or of the highest dignity, were yet such 

 as admirably adapted him for improving chemical science at 

 the time when he lived. What was then wanted, was a wider 

 field of observation ; — an enlarged sphere of chemical phas- 

 nomena; — an acquaintance with a far greater number of in- 

 dividual bodies than were then known ; from the properties 

 of which, and from those of their combinations, tentative ap- 

 proximations to general principles might at first be deduced; 

 to be confirmed or corrected, 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 

 anil 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 



• These charges, especially that of plagiarism, which had liecn unjustly 

 atlvancx'il liy some friends of Dr. IliLTL'ins, wi'r<; triiiiii()hanfly repelled liy 

 I)r. I'rie^llcy, in a paTiiphlct cnlitleil '' Pliilosophical limpirieism," piiblislied 

 in X'lY^. 



2 \\ ■! could 



