SECTIONAL TRANSACTIONS. 
(For reference to the publication elsewhere of communications entered in the 
following lists of transactions, see end of volume, preceding index.) 
SECTION A. 
MATHEMATICAL AND PHYSICAL SCIENCES. 
Thursday, September 7. 
Prof. L. VecarD.—The auroral spectrum and the upper atmosphere (10.0). 
A summary account is given of present knowledge of the auroral spectrum 
and its consequences. 
Most of the results are based on spectrographic work carried out in 
Northern Norway, at Bosekop and Tromsé6 (1912-26), and during the last 
three years important results were obtained at the new Auroral Observatory, 
Tromsé, in collaboration with Mr. L. Harang and Mr. E. Ténsberg. 
In the explored region from 9,000 A.ininfra-red to the limit of atmospheric 
transmission in ultra-violet, 85 bands and lines have been detected. Apart 
from the strong green line and a couple of red lines, probably due to oxygen, 
the auroral spectrum is dominated by nitrogen bands belonging to the negative, 
and the first and second positive, groups. The type of nitrogen spectrum 
agrees well with the theory of Birkeland, that the luminescence is produced 
by electric rays from the sun. The high intensity of the green line is ex- 
plained by assuming oxygen atoms excited through collisions of the second 
kind with active nitrogen, where a kind of resonance effect takes place. 
The auroral spectrum gives no indication of an upper atmospheric layer 
dominated by hydrogen and helium. 
Typical variations within the auroral spectrum have been detected and 
studied. One of these consists of the enhancement of red lines producing 
the red colouring of the aurore. A second is an altitude effect detected in 
1923, one aspect of which is the enhancement, with increasing altitude, of the 
nitrogen bands relative to the green line. 
The temperatures of the emitting molecules of the auroral region were 
quantitatively measured by means of negative nitrogen bands. 
The spectral altitude effect, seen in relation to the height, extension and 
luminescence of the auroral streamers and to the low temperature observed, 
shows that nitrogen must be carried to high altitudes through the effect of 
an electric state set up by the action of a solar radiation of short wave-length. 
The resulting state and the distribution of matter, resembling the sun’s 
corona, is described and shown to fit in with results of radio-echo work, 
and to give a simple explanation of the zodiacal light and the night-sky 
luminescence, agreeing well with spectral observations of Rayleigh and 
Slipher. 
Dr. R. J. VAN pE Graarr.—The electrostatic generation of high voltage 
for nuclear research (10.30). 
