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PHYSICS: A. S. KING 
Proc. N. a. S. 
carried out in which both emission and absorption spectra were compared 
in this way. 
The spectra of calcium and strontium showed in each case a decided weak- 
ening of the enhanced Hues when a mixture of either element with potassium 
or caesium was examined, while the arc lines, presumably due to the un- 
ionized atoms, were unaffected. Barium, with a smaller difference be- 
tween its ionizing potential and that of the added substance, showed a less 
pronounced effect. Sodium, whose ionization potential is nearly the 
same as that of barium, produced no weakening of the barium enhanced 
lines. The experiments thus support the view of an equilibrium between 
electrons and ionized atoms, which may be disturbed by an added supply 
of electrons. 
Certain features of absorption spectra may be described briefly. By 
holding the furnace at a measured temperature and passing through the 
tube a beam of white light from a tungsten filament the absorption spec- 
trum may be readily produced. Turning off the lamp enables the emission 
spectrum of the vapor at the same temperature to be photographed for 
comparison. 
The iron spectrum under these conditons showed no decided difference 
in emission and absorption except as to the production of the ultra-violet 
spectrum. The low temperature stage (1600°-1700° C.) ended in emission 
at X 3440, except that a few scattered lines as far as X 3000 could be brought 
out faintly. The continuous spectrum when a plug is used in the tube at 
the same temperature has about the same limit, and it has been a general 
experience that the emission of vapors in the furnace extends no farther 
than the spectrum of a black body at the same temperature. 
The possibility remained that metallic vapor too cool to emit in the far 
ultra-violet could still show absorption lines if a sufficiently hot source of 
white light in a chamber transparent to the ultra-violet were available. 
Lacking such a source, the light from exploding wires was tried, which 
Anderson has shown to give a continuous spectrum extending to short 
wave-lengths. Dr. Anderson kindly operated the explosion apparatus 
for this experiment, the best results being obtained with wires of lead. 
With the furnace temperature as low as 1600° C, absorption lines of iron 
could be identified as far as X 2298, a limit set by the sensitiveness of the 
photograhic emulsion. These lines had previously been obtained as far 
as X 2447 in the high temperature furnace when the continuous spectrum 
was supplied by a graphite plug in the tube. We thus have the condition 
that for the emission spectrum a definite limit is set by the black body 
radiation at that temperature, but that the vapor is able to absorb radia- 
tion of much shorter wave-length. 
One feature of Saha's theory is that a vapor too cool to emit should be 
able to absorb the lines of the principal series. This was tried with the 
