Biographical Account of [Pjss* 



not fit lum well for theorizing. It is to Franklin and Cavendish 

 that we are chiefly indebted for the electrical theory, such as it 

 is. Epinus also published an excellent work on the subject, 

 which Dr. Priestley must have seen, as he quotes it ; but his 

 mathematical knowledge, I presume, was not suflicient to 

 enable him to understand it. Some important additions might 

 now be made to the theory, in consequence of the discoveries of 

 Volta and Davy; but several points still remain to be cleared up, 

 and they are involved in considerable difficulty. Some of the 

 French writers, particularly Haiiy, still adhere to the old opinion 

 of two electrical fluids ; but in this country every body admits 

 only one fluid. Till lately I considered our hypothesis as far 

 preferable to that of the old theory of Du Faye ; but some of Sir 

 H. Davy's experiments give plausibility to the opposite opinion. 

 This, however, is not the place for enlarging on these difficult and 

 abstruse points, concerning which, I fear, absolute certainty is 

 entirely out of the question. The improvements in electricity, 

 since Dr. Priestley's book appeared, are so numerous and im- 

 portant, that his work in no degree represents the present state 

 of the science : a new history would be requisite. 



His History of the Discoveries relative to Light and Colours 

 was published in IJ/^- it was a much more difficult task than 

 the jformer, and was by no means so successful. It never came 

 to a second edition ; and indeed Dr. Priestley informs us that it 

 cost him a considerable sum of money. The Doctor was by no 

 means fitted for this task. A great part of the subject was ma- 

 thematical ; and controversies had taken place in it, which it 

 was scarcely possible to understand, without a much greater 

 portion of mathematical knowledge than he possessed. Besides, 

 a mathematical subject was much less suited to the characteristic 

 rapidity of Dr. Priestley, who could not- peruse the books on th^ 

 subject in a cursory manner, and was therefore obliged to slur 

 them over altogether. I do not mean to deny that the book 

 possesses considerable value; but had the author not distin- 

 guished himself in other departments, this treatise would not 

 have been sufficient to have brought him into notice. 



As to his Elementary Treatise on Electricity and Natural Phi- 

 losophy, and his book on Perspective, I have never had an 

 opportunity of perusing any of them, and cannot therefore give I 

 any account of them. They are said to be written in a lively i 

 manner, to be very entertaining, and well calculated for enticing j 

 young men to the respective studies. | 



We come now to his chemical labours, to which he was chiefly i 

 indebted for the great reputation which he acquired. No man | 

 ever entered upon any undertaking with less apparent means of I 

 success than Dr. Priestley. He was unacquainted with chemis- I 

 try, excepting that he had some years before attended an elemen- J 



