THE CHEMICAL HISTORY OF AIR. 815 



practically impervious to the winter winds. Here are rookeries of 

 crows, which almost blacken the air as they return from their daily 

 foraging. Here, too, are robins by the thousand. And here, too, 

 in this bird paradise has Mimus polyglottus found a hospitable 

 home. Summer and winter he stays, and with plentiful food and 

 warm shelter he bids adieu to his migratory instincts. Such in 

 former days we may believe was the condition of the virgin forests 

 of New Jersey. 



^bc Cbcmical Ibietor^ of Bin 



AT the Sanitary Congress, at Portsmouth, Dr. W. J. Russell, 

 the President, delivered an interesting address upon this 

 subject, from which we extract the following : — " The 

 properties and phenomena of air were to a great extent known to 

 the ancients, but it was not until the seventeenth century was well 

 advanced that an English chemist, Hooke, in 1665, discovered 

 that what Boyle and the great Bacon thought a ' volatile nitre,' 

 or a ' crude and windy ' spirit in the air, was really oxygen. A 

 hundred years later, Priestley re-discovered what Hooke and his 

 successor, Mayhew. had already found out ; but scholars had by 

 that time become inoculated with the spirit of science, and there 

 was no longer any fear that the truth would ever again be lost. 

 Our means of analysing the gases of the air, and every other gas, 

 remained comparatively imperfect until 1857, when Bunsen's 

 great work on ' Gas Analysis ' was published — a work which 

 remains still a monument to its author's ingenuity and skill. But 

 it was not until the second half of the nineteenth century had 

 been advanced that the existence and importance of air-dust was 

 suspected, and it was to the acuteness of Mr. Aitkin that we 

 owed the discovery of how important a part air, pure and impure, 

 would play in sanitary science. 



He discovered air-dust in the spray from the sea, in the rari- 

 fied atmosphere on the summit of the Rijhi, impurities at the top 

 of the Eiffel Tower, and dust in the fogs and mists. ' If there 



