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IOWA ACADEMY OF SCIENCE Vol. XXIX, 1922 
frequencies from 10 5 to 10 7 , current using electrode distances 
from 5 to 30 mm. and gas pressures from 1 to 5 mm. of mercury. 
For a specified gas pressure and electrode distance the direct po- 
tential and the maximum value of the radio frequency potentials 
were found to be the same. In the light of this result theoretical 
consideration indicated that the luminosity was started by colli- 
sions of electrons, rather than of gaseous ions, with the gas mole- 
cules. 
The flashes of light from hydrogen, oxygen, argon and air in 
turn excited by damped radio frequency current were found to 
be each a train of radio frequency flashes when examined by 
means of a rotating mirror. For hydrogen and argon the first 
few flashes of the radio frequency train showed a predominance of 
the green and blue lines of the spectrum, the later flashes of the 
train showed a predominance of the red lines. This was as- 
cribed to the fact that the maximum value of the current in the 
first few cycles of the damped discharge was much greater than 
in the subsequent cycles. 
State University oe Iowa. 
THE BROADENING OF THE BALMER LINES OF HY- 
DROGEN WITH PRESSURE 
E. O. HULBURT 
Abstract 
Spectrograms were taken of H/3, HY and HS of hydrogen ex- 
cited by condensed discharges for gas pressures from 2 to 135 
mm. of mercury. At the highest pressure the photographic widths 
of the lines were nearly 100 A.U. Throughout the series of pres- 
sures the intensity of the central portions of H/2 was maintained 
sensibly constant. Assuming that the widening was caused by dis- 
turbance of the uniformity of the radiation due to collisions of 
the radiating particles (as proposed by others), the widening of 
the lines with pressure was calculated and found to be consider- 
ably less than that observed. This result indicated that the 
assumption was inadequate, and that the widening should be 
attributed to other causes such as the effect of the electrical 
fields, as investigated by Merton (Proc. Roy. Soc., 92, 322, 1915). 
State University oe Iowa. 
