164 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Photographic Observations of the "Flash" Spectrum. 



The photographic investigation of the "flash" spectrum begun in the early 

 part of 1909 by Mr. Hale and Mr. Adams has been continued throughout 

 the year. In a communication read at the Cambridge meeting of the Astro- 

 nomical and Astrophysical Society of America, August 1910, some of the 

 results obtained were summarized. Among these may be mentioned the 

 following : 



(i) About 1,200 bright lines have been photographed and their positions 

 measured between A 4400 and A 6600. Of these about 97 per cent have been 

 identified with reasonable certainty with dark lines given in Rowland's table 

 of the solar spectrum. 



(2) Double reversal seems to be practically a universal characteristic of 

 chromospheric lines at points close to the sun's edge. 



(3) There can be no systematic shift greater than 0.002 Angstrom between 

 the average of the wave-lengths of the bright lines and the corresponding 

 dark lines in the solar spectrum, 



(4) The enhanced lines are relatively very much stronger as bright lines 

 in the chromosphere than as dark lines in the solar spectrum. 



(5) Cobalt, titanium, and vanadium show the greatest number of bright 

 lines of any of the elements in the solar spectrum except carbon. 



The large image and powerful spectroscopic equipment of the 150- foot 

 tower should be especially favorable for the continuation of this investigation. 



Miscellaneous Investigations. 



A self-recording declination magnetograph has been in regular operation 

 on Mount Wilson since the spring of 1909, with the exception of a few 

 months during the winter season. The instrument is in charge of Mr. Bab- 

 cock. The chief value of the record lies in the nature of the disturbances 

 observed near the time of transit of sun-spots across the solar meridian. 

 The greater part of these disturbances are found to occur about 24 hours 

 after the transit. Perhaps the best example of this kind was that accompany- 

 ing the spot which crossed the solar meridian on August 9, 1909. Twenty- 

 four hours later the magnetic declination suddenly increased 40', remained 

 almost stationary for several hours, and then returned to its normal value. 

 On the following day at about the same hour the declination suddenly de- 

 creased about 25', but did not remain displaced. 



No unusual effects were noted during the proximity of Halley's comet. 



By means of a Dolazalek quadrant electrometer observations were made 

 by Mr. Babcock of the diurnal variation of the atmospheric potential preced- 

 ing and during the transit of Halley's comet. 



M. Henri Chretien devoted a considerable amount of time during the ear^ 

 lier part of this year to a theoretical investigation of an electromagnetic 

 theory of the law of the sun's rotation. He also did a large amount of obser- 

 vational work with the 5-foot spectroheliograph and the 30-foot spectrograph. 



