40 REPORT— 1902. 



nature of the upper air. On passing electric discharges through the 

 tubes containing the most volatile of the atmospheric gases, they glow 

 with a bright orange light, which is especially marked at the negative 

 pole. The spectroscope shows that this light consists, in the visible part 

 of the spectrum, chiefly of a succession of strong rays ia the red, orange, 

 and yellow, attributed to hydrogen, helium, and neon. Besides these, 

 a vast number of rays, generally less brilliant, are distributed through 

 the whole length of the visible spectrum. The greater part of these 

 rays are of, as yet, unknown origin. The violet and ultra-violet part of 

 the spectrum rivals in strength that of the red and yellow rays. As 

 these gases probably include some of the gases that pervade inter- 

 planetary space, search was made for the prominent nebular, coronal, and 

 auroral lines. No definite lines agreeing with the nebular spectrum could 

 be found, but many lines occurred closely coincident with the coronal 

 and auroral spectrum. But before discussing the spectroscopic problem 

 it will be xiecessary to consider the nature and condition of the upper 

 air. 



According to the old law of Dalton, supported by the modern dynamical 

 theory of gases, each constituent of the atmosphere while acted upon by 

 the force of gravity forms a separate atmosphere, completely independent, 

 except as to temperature, of the others, and the relations between the 

 common temperature and the pressure and altitude for each specific 

 atmosphere can be definitely expressed. If we assume the altitude and 

 temperature known, then the pressure can be ascertained for the same 

 height in the case of each of the gaseous constituents, and in this way 

 the percentage composition of the atmosphere at that place may be 

 deduced. Suppose we start with a surface atmosphere having the com- 

 position of our air, only containing two ten-thousandths of hydrogen, then 

 at thirty-seven miles, if a sample could be procured for analysis, we 

 believe that it would be found to contain 1 2 per cent, of hydrogen and 

 only 10 per cent, of oxygen. The carbonic acid practically disappears ; 

 and by the time we reach forty-seven miles, where the temperature is 

 minus 132 degrees, assuming a gradient of 3 2 degrees per mile, the 

 nitrogen and oxygen have so thinned out that the only constituent of 

 the upper air which is left is hydrogen. If the gradient of temperature 

 were doubled, the elimination of the nitrogen and oxygen would take 

 place by the time thirty-seven miles was reached, with a temperature of 

 minus 220 degrees. The permanence of the composition of the air at the 

 highest altitudes, as deduced from the basis of the dynamical theory of 

 gases, has been discussed by Stoney, Bryan, and others. It would appear 

 that there is a consensus of opinion that the rate at which gases like 

 hydrogen and helium could escape from the earth's atmosphere would be 

 excessively slow. Considering that to compensate any such loss the same 

 gases are being supplied by actions taking place in the crust of the earth, 

 we may safely regard them as necessarily permanent constituents of the 

 upper air. The temperature at the elevations we have been discussing 



