[OSEPH PRIESTLE Y. i ;: 



a detailed view of the extensive and beneficial effects of this 

 habitude in the grand economy of nature. '-From observing 

 the analogy between the cessation of expansion by the ther- 

 mometer during the liquefaction of the ice, and during the 

 conversion of water into steam, Dr. Black having explained the 

 one, thought that the phenomena of boiling and evaporation 

 would admit of a similar explanation. He was so convinced of 

 the truth of this theory, that he taught it in his lectures in 1761, 

 before he had made a single experiment on the subject. At 

 this period, his prelections on the subject of evaporation were 

 of great advantage to James Watt, afterwards 30 distinguished, 

 who made use of them in his application of steam power. 

 I'lack's discovery, indeed, may be said to have laid the founda- 

 tion of that great practical use of steam which has conferred so 

 great a blessing upon the ]3resent age." 



JOSEPH PRIESTLEY. 



Josejih Priestley, a Dissenting divine, but more justly eminent 

 as a philoso*pher, was born on the i8th of March, 1733, near 

 Leeds. 



At Warrington, where he occupied the post of tutor in an 

 academy, he first began to acquire reputation as a writer in 

 various branches of literature. In 1767, he gave to the world 

 his History of Electricity. It is rather carelessly and hastil}' 

 executed, but must have been of advantage to the science. 

 Almost the whole of his historical facts are taken from the 

 Philosophical Transactions ; but at the end he gives a number 

 of original experiments of his own. The most important of all 

 his electrical discoveries was that charcoal is a conductor of 

 electricity, and so good a conductor that it vies even ■^^'^th 

 the metals themselves. This publication went through several 



