356 HISTORY OF SCIENCE. 



remarked tnat he believed other changes were destined to take place 

 which would still more affect the progress and the happiness of mankind. 

 Perhaps it was such expressions as these that suggested to some of 

 those concerned in that great convulsion, the French Revolution, that 

 Priestley should be honoured at their hands ! It is certain that he 

 received the title of Citizen of the Republic, and was even made an 

 honorary member of the National Convention. These nominal dis- 

 tinctions brought disaster upon the unfortunate philosopher. When 

 the minds of men were unsettled by the progress of events in France, 

 the fury of a Birmingham mob was aroused against Priestley and some 

 of his political friends, and on the i4th of July, 1791, the populace 

 attacked a place where a few of these friends were assembled to cele- 

 brate the anniversary of the downfall of the Bastille ; and when they 

 had spent their fury upon the house of meeting, they proceeded to 

 Priestley's house, which he on that day had not quitted. Priestley 

 took refuge in a neighbour's house, and witnessed the wreck of his 

 dwelling, which was set on fire. His library, his scientific instruments, 

 his manuscripts, were soon turned into a heap of ashes, and he had 

 probably a narrow escape with his life. He removed to London, but 

 found that he was in some sense a marked man. He entertained, 

 rightly or wrongly, the opinion that the Birmingham mob was arti- 

 ficially excited by concealed agents of the Government of the day. 

 He was therefore again compelled to carry forth his household gods, 

 and as under such circumstances his residence in England became 

 unendurable, he quitted for ever his native land, and, in his sixty-first 

 year, embarked in 1795 for America. He died in 1804 at Northum- 

 berland, a small town on the Susquehanna, a few hours after he had 

 arranged all his literary concerns and inspected the proof sheets of 

 his last theological work. 



It was in 1772 that Priestley published his first "Observations on 

 Different Kinds of Air" in the "Transactions of the Royal Society." It 

 will be readily understood from what has gone before, that the expres- 

 sion " different kinds of air " means, as we say now, the different gases. 

 The first gas studied by Priestley was carbonic acid, and he tells how, 

 when living near a brewery, he became curious about the nature of 

 the gas which was given off during fermentation. His experiments 

 with carbonic acid did not add much to the knowledge of fixed air, 

 except in respect to his discovery that, when condensed by pressure, 

 a much larger quantity of the gas is absorbed by water. He was 

 thus, in fact, the discoverer of the method of preparing the well-known 

 beverage, soda-water. 



" There are, I believe, ver> fe\\ maxims in philosophy that have laid 

 firmer hold upon the mind than thai air, meaning atmospheric air 

 (free from various foreign matters, which were always supposed to be 

 dissolved in and intermixed with it), is a simple elementary substance, 

 indestructible and unalterable, at least as much so as water is supposed 



