l62 REPORTS ON INVESTIGATIONS AND PROJECTS. 



The continuation of the study of the Zeeman effect in sun-spots and the 

 knowledge that many of the lines affected in spots are most complicated in 

 structure and require very powerful spectroscopic apparatus for complete 

 resolution has made it desirable to revise to some extent the general cata- 

 logue of the spot-spectrum according to the results obtained with the spec- 

 trograph of the 1 50- foot tower telescope now under construction. Accord- 

 ingly definitive publication of the catalogue is being delayed for this reason. 

 A summary of some of the more general results, however, has been pub- 

 lished by Mr. Adams during the past year. Among the conclusions the fol- 

 lowing may be included : 



(1) About 14,000 lines are contained in the catalogue, of which 11,000 

 have been measured and the wave-lengths determined independently. 



(2) About 5,000 lines present in the spot-spectrum have been identified 

 as due to titanium oxide. About 600 lines have been identified by Mr. 

 Olmsted as due to calcium hydride. 



(3) A detailed study of the iron lines affected in the spectrum of sun- 

 spots and comparison with the results obtained for the same lines in labora- 

 tory spectra of the flame and center of an iron arc strengthens the view 

 brought forward several years ago by Fowler, and by Hale and Adams, that 

 the observed phenomena may be accounted for satisfactorily on the basis of 

 a reduction of temperature in sun-spots. The weakening of the enhanced 

 lines in the spectrum of sun-spots points to the same conclusion. 



(4) The existence of a magnetic field in sun-spots explains in a most 

 satisfactory way the presence of the large number of lines which are greatly 

 widening or show doubling or tripling in the sun-spot spectrum. 



The radial movement of the vapors in sun-spots, first discovered by Ever- 

 shed, has been confirmed during the past year by Mr. St. John. He is con- 

 tinuing the investigation with the spectrograph of the 60-foot tower tele- 

 scope, using an auxiliary device by means of which spectra of different por- 

 tions of the spot may be brought side by side upon the photographic plate 

 for purposes of measurement. 



Investigation of Displacements of Spectrum Lines at the Sun's Limb. 



An investigation of the displacements at the sun's limb of 470 selected 

 lines has been published by Mr. Adams during the year. Some of the prin- 

 cipal results found are as follows : 



( 1 ) The displacements are very small for certain high-level elements, such 

 as hydrogen, sodium, magnesium, and calcium. Also for certain elements 

 of very high atomic weight, such as lanthanum and cerium. 



(2) The displacements for titanium, vanadium, and scandium are con- 

 siderably smaller than those for iron and nickel. 



(3) The enhanced lines as a class show decidedly larger displacements 

 than the arc lines. 



(4) The lines most strengthened at the limb usually show small displace- 

 ments. 



