212 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 193 3 



others in the ultraviolet. Recent remarkable progress in atomic 

 physics has proved that the spectrum lines of a chemical element do 

 not all refer to the atoms of that element in a complete state. Atoms 

 when highly excited by intense heat, radiation, or electricity may 

 temporarily lose one or more electrons. Some of their spectral lines 

 refer to the fragments more or less diminished which remain with 

 the nucleus of the atoms so excited. The H and K lines of calcium, 

 for example, represent ionized calcium atoms with one electron gone. 



The sun and the stars are all moving rapidly with reference to one 

 another through space. About the year 1910 L. Boss and W. W. 

 Campbell independently showed that the sun is moving at about 12 

 miles per second toward a well-defined point in the constellation 

 Hercules, about 10° southwest of the bright star Vega. In Camp- 

 bell's determination the frame of reference was fixed by the positions 

 of 280 bright stars. Later, in 1926, Campbell and Moore employed 

 2,119 stars in determining the solar motion. Many of the stars form 

 double, triple, or even more complex systems, revolving with respect 

 to the center of gravity of the components, as well as traveling 

 rapidly through space together. All such motions, including the 

 motion of our sun toward Hercules, express themselves in the spectra 

 by shifting the positions of all the spectral lines of the moving 

 luminaries. The lines shift toward the red when the star is receding 

 (see pi. 3), and toward the violet when it is approaching us, or 

 what amounts to the same thing, when we are receding from or 

 approaching the stars. Astronomers, by measuring these line shifts 

 accurately, can estimate the velocities of stars away from or toward 

 the sun, as the case may be. In the case of double stars, with short 

 periods of mutual revolution, the spectral lines shift alternately 

 toward the red and toward the violet, and betray the exact period 

 of rotation, and in some cases the diameter of the star's orbit. 



Some 27 years ago Hartmann ^ first observed, in the spectroscopic 

 binary 8 Orionis, that the H and K lines of calcium did not share 

 in the orbital velocity oscillations of the hydrogen and helium lines 

 arising in the stellar atmosphere, but remained relatively fixed in 

 position, hence the name " stationary " calcium lines, which has per- 

 sisted almost to the present time. By far the most suggestive and 

 penetrating early contribution to the problem of the stationary H 

 and K lines was given by V. M. Slipher ^ in 1909. 



Slipher measured the velocities given by the stationary calcium 

 lines in 10 bluish stars in the constellations Scorpio, Ophiuchus, 

 Perseus, and Orion. From observations of ^ and <»■ Scorpii, double- 

 lined spectroscopic binaries (both components being bright enough 



«Astrophys. Journ., vol. 19, p. 268, 1904. 

 s Lowell Obs. Bull., vol. 2, p. 1, 1909. 



