MOUNT WILSON SOLAR OBSERVATORY. 245 



(52) The inner vapor of a powerful condensed spark produces dis- 

 symmetries of spectrum lines giving apparent displacements toward 

 the red; the lines of the outer vapor coincide with the arc lines. 



(53) Comparisons between the center and negative pole of the iron 

 arc have been made for 1,600 lines. For 1,300 of these the wave- 

 lengths are independent of the distance from the pole and the current 

 strength. 



(54) For 250 lines the wave-lengths at the negative pole exceed those 

 at the center by 0.015 a or more; for 50 lines they are less at the pole. 



(55) The differences vary with the current, a change from 5 to 7 

 amperes giving measurable shifts for lines of negative displacement. 



(56) The displacements are indirectly related to pressure shifts; 

 provisionally, they are attributed to changes in density. 



(57) Because of these circumstances, the wave-lengths of the ques- 

 tionable lines among the tertiary standards and the international 

 secondaries are being redetermined under standard conditions. 



(58) Measures of the Zeeman separation of 769 iron, 903 chromium, 

 and 643 vanadium lines have been made from plates taken usually 

 with field-strengths of about 30,000 gausses. 



(59) Three series of determinations of ejm give a mean value of 

 1.761, with an uncertainty of 2 units in the third decimal. 



STAFF. 



In addition to his general duties, the Director has devoted special 

 attention during the year to investigations of solar magnetic and 

 electric phenomena, including a preliminary attempt, in conjunction 

 with Mr. Babcock, to detect the Stark effect in sun-spots and other 

 regions of the solar atmosphere. Dr. Walter S. Adams has continued 

 his duties as Assistant Director and head of the department of stellar 

 spectroscopy, and has carried on extensive studies of stellar spectra 

 and the spectrum of the chromosphere. Professor Frederick H. Scares, 

 in addition to his services as superintendent of the Computing Division 

 and editor of the Observatory publications, has continued and extended 

 his researches in stellar photometry and his work on the general mag- 

 netic field of the sun. Dr. Arthur S. King, superintendent of the 

 physical laboratory, has devoted most of his time to the study of 

 furnace, arc, and spark spectra. Dr. Charles E. St. John has continued 

 his investigations on standards of wave-length and the determination 

 of levels, pressures, and velocities in the solar atmosphere. Mr. 

 Harold D. Babcock has collaborated with Dr. St. John in the study 

 of wave-length differences in various parts of the arc, pushed forward 

 his studies of the Zeeman effect, with special reference to the determi- 

 nation of e/m, and taken part in various other investigations. Mr. 

 Ferdinand Ellerman has taken many solar photographs of various 

 kinds with the 150-foot tower telescope and continued his duties as 



