34 LOEWENFELD, Coutributiojis to the History of Science. 



It might appear perhaps superfluous to give /// toto a 

 letter deah'ng chiefly with reHgious writings. The only 

 object is to show that Priestley was a preacher and theo- 

 logian in the first instance, and only in the second instance 

 a natural philosopher. 



The year 1774 is the one in which he discovered 

 ammonia, and it is probably to this most important 

 discovery that he refers in the little sentence about his 

 philosophical pursuits sandwiched between all the com- 

 munications on religious subjects. 



The second letter which I have is quite similar to the 

 one communicated above. It is dated London, 10/1/1775, 

 and — in four pages taken up almost entirely with religious 

 topics — there is just this one sentence : — 



" A new edition of my treatise on air is in the press, 

 and I have made so many additions to my observations 

 that I propose to publish a supplement to that work 

 before I leave London. But the more I do, the more I 

 see is to be done." 



The various volumes of his " Experiments and Obser- 

 vations on different kinds of air," the work referred to 

 here and in the previous letter, were published in the years 

 1774' 1775. ^777^ 1779. 1780 and 1786. This work, of 

 which Davy^^ said "that he knew no book so likely to 

 lead a student into the path of discovery as Dr. Priestley's 

 six volumes on air," ib now very rare, at least in its 

 original edition. It was reprinted in 3 volumes in 1790. 



The departure from London refers to a journey which 

 Priestley made with Lord Shelbourne to Planders, Holland, 

 Germany and Paris. 



In the year 1780 Lord Shelbourne intimated to Priestley 

 that he had no further need for his services. Priestley con- 

 sequently took up his residence in Birmingham, where he 

 became a minister of the so-called New Meeting. 

 ^* Davy's ' Collected Works,' vol. vi., p. 117. 



