ASTRONOMY: A. 5. KING 
371 
determined. Such speculations, though they are very interesting, can- 
not be given any great weight. There is still a considerable region be- 
tween wave length 600 and wave length one which must be experiment- 
ally explored. 
My present limit is set by the adjustment and dimensions of my ap- 
paratus. Now that we know that a Schumann plate can be used and 
that a speculum grating is efficient, I see no insuperable difficulty to a 
still further extension by purely spectroscopic means. 
1 The Spectroscopy of the Extreme Ultra-Violet, Longmans, Greene & Co. 
2 J. J. Thomson, Phil. Mag., London, 28, 620 (1914); E. R. Ladd, Ann. Physik, Leipzig, 
46, 605 (1915). 
3 Berlin, Verh. D. Physik. Ges., 15, 560 (1913). 
UNSYMMETRICAL LINES IN TUBE-ARC AND SPARK SPECTRA 
AS AN EVIDENCE OF A DISPLACING ACTION 
IN THESE SOURCES 
By Arthur S. King 
MOUNT WILSON SOLAR OBSERVATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Presented to the Academy, April 15, 1915 
The most effective laboratory means of causing a displacement of 
spectrum lines is pressure around the light-source, which has been 
found to be generally effective in changing the wave-length of lines in 
the spectra of the arc, spark and electric furnace. These displacements 
vary in magnitude for different groups of lines at the same pressure. 
Recently other influences have been found effective in causing small 
displacements, these manifesting themselves usually in making the 
spectrum lines unsymmetrical, usually with the red side stronger. A 
measurement of the maximum of the line under these conditions gives 
a different wave-length from that obtained for the same Hne when 
symmetrical. 
We have then the two-fold problem of finding what features in the 
light-source produce these diss)anmetries and the degree to which 
various lines are subject to such disturbing influences. 
About two years ago, the writer described the spectrum of the Hube- 
arc, ' and noted that many lines were made highly unsymmetrical in 
this source. The tube-arc is obtained when the tube used in the electric 
furnace is made thin at its middle so that when the voltage is applied 
the tube quickly burns apart, forming an arc which carries a very large 
current at low voltage. This ring of arc is viewed axially and the 
spectrum shows many peculiarities. 
