206 CARNEGIE INSTITUTION OF WASHINGTON. 



observations, and have a probable error of less than 0.001 a. The measure- 

 ments of St. John and Babcock have contributed in an important degree to 

 this valuable collection of material, and the difficult task of combining and 

 weighting the observations has in large measure been carried on by St. John 

 as chairman of the Commission of Standards of Wave-Length (p. 214). 



In continuation of their previous work, St. John and Babcock have measured 

 the wave-lengths of several hundred solar lines, with the double purpose of 

 securing standards for the revision of the table of solar-spectrum wave-lengths, 

 and studying the relative displacements of the lines in sun and arc which 

 form so essential a test of the generalized theory of relativity. The com- 

 plicated variety of phenomena in the sun which may give rise to the dis- 

 placements of lines requires extensive investigation, and the study of the shift 

 between center and limb is well adapted to throw light on some of these diffi- 

 cult questions. The powerful spectroscopic apparatus of the 150-foot tower 

 telescope and an interferometer used in conjunction with the Snow telescope 

 are being emp^ed in the measurement of these small displacements (p. 215). 



St. John, assisted by Miss Ware, has continued throughout the year his 

 study of the solar rotation. No measurable change has been detected during 

 the 8 years now covered by his observations, but they will be extended to 

 include a complete sun-spot cycle. Especial attention is being given to the 

 rate of rotation in high latitudes, where it now seems probable that Faye's 

 formula does not fully represent the results of observation (p. 217). 



Russell, King, and Noyes have obtained important results supporting the 

 validity of Saha's theory of ionization in solar and stellar atmospheres. 

 Barium is highly ionized in the reversing layer of the sun, and even in spots, 

 though neutral atoms are also present. Russell has explained on theoretical 

 grounds why it is more highly ionized than sodium, in spite of the equality of 

 their ionizing potentials. King has confirmed in the electric furnace Saha's 

 prediction that the enhanced lines of calcium, strontium, or barium, obtained 

 when these elements are vaporized alone or in the presence of elements having 

 equally high ionizing potentials, are not visible when substances like potas- 

 sium or caesium, of lower ionizing potentials, are vaporized with them. He 

 has also found, in harmony with Saha's theory, that a mass of gas too cool to 

 emit light is still able to absorb lines of the principal series (p. 246). King 

 has photographed the absorption spectrum of iron at 1600° as far as X2298, 

 though the emission spectrum for the same temperature ends at X3440 (p. 247). 

 He has also found that the A and B bands of oxygen in the solar spectrum can 

 be produced in the laboratory by the absorption of air columns only 7 and 40 

 meters long, respectively. The water-vapor band a was observed with an 

 air-path of only 9.5 meters, under conditions of low humidity (p. 250). These 

 results have an important bearing on the question of the presence of oxygen 

 and water-vapor in planetary atmospheres. 



The above results were obtained with the new and very effective vacuum 

 furnace. The old furnace is being used by King, in collaboration with Noyes, 

 in a study of the conductivity of vapors at high temperatures (p. 248). It is 

 especially well adapted for such work because of the high temperatures avail- 

 able, the control which may be kept over the temperature and other conditions 

 during the experiments, and the ease with which the concentration of the vapor 

 may be varied. In the work so far carried on with the chlorides of calcium, 



