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DEVELOPMENT OF METEOROLOGY——ABBE. 29% 
small amount of fixed air. The next step in the separation of the 
gases in our atmospheric mixture was due to Rutherford, a pupil 
of Black, who in 1772 announced the discovery of nitrogen as the 
residual gas after the combustion of carbon and the absorption of 
the resulting fixed air. The discovery of oxygen was made inde- 
pendently and nearly simultaneously by Priestley and Scheele; but 
Priestley published his results in 1775, a year before Scheele. The 
recognition of oxygen as an independent gaseous element and the 
establishment of our modern view of the air as a simple mixture is 
due to Lavoisier, who published several memoirs on the subject in 
1777 and 1778, while Cavendish was carrying on a parallel system of 
experiments in England, experiments that he began in 1777, but 
published only some years later. 
With the discovery of nitrogen and oxygen in the atmosphere 
and the measurement of the exact ratios of these and various so- 
called impurities, the chemistry of the atmosphere halted until, in 
1882, Lord Rayleigh began a research on the relative densities of 
hydrogen, oxygen, and other gases, concluding in 1893 by the state- 
ment that nitrogen obtained from the atmosphere was somewhat 
denser than nitrogen prepared from ammonia, and that the difference, 
though shght, was so far beyond all question that 1t demanded an ex- 
planation. ‘This explanation was announced in a preliminary way in 
August, 1894, but was received with such incredulity that one chem- 
ist sarcastically inquired *“ whether the name of the new gas had also 
been discovered.” But the matter was brought to a clear demon- 
stration by diffusing the mixed gases slowly through a long train 
of tobacco pipes of the variety known as the “ church-warden pipe,” 
which is made of a very fine clay through which diffusion proceeds 
very slowly. Thus argon was discovered. Of course you will recog- 
nize the fact that this last step in the analysis of atmospheric air 
is not a chemical but a physical process, illustrating the general 
statement that no one branch of science can endure or progress 
without the assistance of correlated friendly branches. 
The discovery of argon paved the way to new ideas in regard to 
the structure of the molecules of gases, ideas that threaten entirely 
to undermine some portions of the old kinetic theory of gases. 
Since the discovery of argon, chemists and physicists, working long 
different lines, have, as you know, devised methods of producing 
extremely low temperatures; so that atmospheric air, and even hydro- 
gen, have been liquefied, and by the help of these extremely cold 
liquids other gaseous constituents have been discovered in the atmos- 
phere. First, heliwm was discovered by its lines in the solar spec- 
trum; then it was evolved from a rare mineral, named cleavite. and 
finally it was shown to be present in our atmosphere. Then a large 
mass of air was cooled down to its boiling point, and in the residue 
