98 The Ottawa Naturalist. 



position by weight and by volume of the atmosphere. This was in 1781. 

 It is supposed that Cavendish made no less than 400 analyses of the air. 

 The mean result of his labours was that too volumes of air contain 

 20.83 parts by volume of oxygen. 



Since that time Gay-Lussac and Humbolt, Davy, Thomson, 

 Kuppfer and, later by more accurate methods, Regnault, Bunsen, 

 Lewy, Stas, Dumas, Boussingault and others, have carefully analysed 

 the air. Their results serve practically to corroborate those of Cavendish. 



It is now well known that the amount of oxygen in normal air 

 varies at different times and in different localities, but the work of all 

 the most careful investigators goes to show that the limit of variation 

 lies within 20.9 and 21.0 volumes of oxygen per 100 of air. Consider, 

 ing this, we may well marvel at the high degree of accuracy of this 

 quantitative work of Cavendish more especially when we think of the 

 apparatus and methods of his day. 



For more than a hundred years then, it has been thought that the 

 atmosphere consisted chiefly of a mixture of the elementary gases, 

 oxygen and nitrogen. We have also for many years recognized as 

 present in the aerial ocean that envelopes our globe, small and variable 

 quantities of carbonic acid [3 to 4 volumes per 10,000] and vapour of 

 water. Under artificial circumstances, traces of sulphuretted hydrogen, 

 ammonia, nitric and other acid?, organic matter, etc., are noticed. 



We now have to chronicle a further step in our knowledge of the 

 atmosphere's composition. 



Lord Rayleigh, the eminent English physicist, and William Ram- 

 say, professor of chemistry at University College, London, at the meet, 

 ing of the British Association held in Oxford in August last, surprised 

 the world scientific and lay by the announcement that they had 

 discovered another atmospheric constituent. 



To give you some idea how these scientists came to make the 

 discovery of this constituent which the weight of the proof 

 indicates to be an element hitherto unknown I shall make 

 tree use of an abstract of a paper read by them before the Royal Society 

 on the 31st of January of the present year. Priestley had discovered 

 oxygen by chance ; the present discovery was the result of an elaborate 



