Vol. 8, 1922 
PHYSICS: G. R. HARRISON 
261 
condensation of the vapor and coating of the windows, sHts were placed 
at each end of the hot column and kept at a red heat. A mercury manom- 
eter was kept permanently connected to the main tube, which could be 
exhausted to a cathode ray vacuum in three minutes with a Gaede cylinder 
pump. Temperatures were measured with a thermocouple calibrated by 
the Bureau of Standards. A cadmium spark in air was used as a light 
source, supplemented by electrically exploded wires of various metals in 
regions where Cd emission lines interfered. For photographing the trans- 
mitted light a Fery spectrograph made by Hilger was used, having a range 
2100 to 6000 Angstroms, and a dispersion sufficient to resolve the lines 
to w = 32 in Na. 
1l 
X 
* -> 
1 
( 
&/00 3000 
a. Temp. JSO°C. Pressure Zcm. hyc/ro^en 
X. 
Z/OO 36ao 
b. Temp. ^T^^C, Pressure 3cm. hi^cfrogten 
r 
n 
^ — ^ 
Z/OO ,3000 -^oo ^oao 
c. Temp. S40''C. Pressure -^cm. hycfro^en 
FIG. 1 
Curves showing the relation of absorption at different wave-lengths to vapor density 
in saturated sodium vapor, with hot column 30 cm. long. Hydrogen pressures from 
1 to 400 mm. had no apparent effect. 
• 
Results with Sodium. — The continuous absorption was found to be much 
more pronounced in certain pictures than in others, but the only determin- 
ing factor seems to be vapor density. The presence of hydrogen in pres- 
sures from one to 400 mm. had no visible effect. The absorption begins at 
the last resolved line of the principal series, which is about five Angstrom 
units from the theoretical head. No definite break is observable, which 
is to be expected, since in the region near the limit there is an integrated 
