THE DEVELOPMENT OF METEOROLOGY. 41 
gard 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, chem- 
ists and physicists, working along different lines, have, as 
you know, devised methods of producing extremely low tem- 
peratures; so that atmospheric air, and even hydrogen, 
have been liquefied, and by the help of these extremely cold 
liquids other gaseous constituents have been discovered in the 
atmosphere. First, helium was discovered by its lines in the 
solar spectrum; 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 krypton was discovered. 
Finally argon was also cooled down to its boiling point and 
neon was discovered. The separation of neon from helium 
requires the very low temperature of boiling hydrogen, or 
20.5° on the absolute scale. Although these new gases occur 
in our lower atmosphere only in very minute quantities, yet 
there is some reason to believe that eventually they will play 
an important part in explaining some of the electrical phe- 
nomena that are at present quite mysterious. It has been 
independently suggested by Huyghens and Schuster that the 
brilliant green line in the spectrum of krypton is probably 
identical with the green line in the spectrum of the terres- 
trial aurora borealis, showing that krypton may exist in our 
upper atmosphere or in the adjoining celestial space. 
But we have not finished with the gases of our atmosphere, 
for in 1898 Madame Curie announced the isolation of two 
new substances, polonium and radium. These furnish an 
emanation, which consists of gaseous particles, among which 
is helium, which latter also emanates from the element 
thorium. Numerous other substances are now known to 
send out such emanations, each of which resembles some of 
the inert gases of the atmosphere. It seems probable that 
these emanations represent the degeneration of molecules of 
the complex elements into simpler molecules or even into 
elementary matter, if such there be, thus leading to a great 
expansion of our ideas as to molecular structure. As these 
