SOLAR OBSERVATORY. 137 



tions to furnish all the data required in the solution of its own problems. 

 Furthennore, the value to physics or astronomy of the results it may attain 

 in these fields will be increased by their correlation with astrophysical phe- 

 nomena. 



It is expected that Professor Kapteyn will spend a portion of each year 

 with us, and have charge of such parallax and similar work as may be done 

 with the large reflectors. Although these instruments must be devoted, for 

 the most part, to spectrographic observations and the photography of 

 nebulae, I believe that they may also yield important contributions to 

 Kapteyn's cooperative undertaking. 



STAFF. 



Throughout the year Mr. W. S. Adams has remained in charge of the 

 computing division, while Mr. G. W. Ritchey has continued his work as 

 superintendent of construction. Dr. Henry G. Gale, who spent a portion of 

 last year on Mount Wilson, returned to the University of Chicago in 

 September, 1906. Mr. Ferdinand Ellerman, assisted occasionally by Dr. 

 Charles M. Olmsted, has continued to take the daily series of photographs 

 with the Snow telescope and the 5-foot spectroheliograph. He has also 

 made various photographs of sun-spot spectra, and has done much general 

 photographic work. Mr. Olmsted has spent most of his time in laboratory 

 investigations, but has also made a series of pyrheliometric observations in 

 continuation of Mr. Abbot's work on Mount Wilson. Dr. H. K. Palmer, 

 who was engaged in holographic investigations with the Snow telescope 

 during the summer of 1906, resigned his position in September. Miss Louise 

 Ware and Miss Ruth E. Smith have continued their work in the computing 

 division. Miss Jennie B. Lasby and Miss Cora G. Burwell were appointed 

 computers in October, 1906, and July, 1907, respectively. 



Prof. W. H. Julius, of the University of Utrecht, was engaged in special 

 investigations on Mount Wilson during the summer of 1907. 



INVESTIGATIONS IN PROGRESS. 



The investigations in progress during the past year include: (i) Daily 

 photography of the sun vvith the photoheliograph ; (2) daily photography of 

 the sun with the spectroheliograph; (3) photography of the spectra of sun- 

 spots; (4) photographic comparisons of the spectra of various parts of 

 the sun's disk; (5) spectrographic investigations of the solar rotation; (6) 

 laboratory investigations; (7) pyrheliometric observations; (8) magnetic 

 observations with a recording variometer. 



No important modifications have been made in the Snow telescope, except 

 that it has been found advantageous to blow all of the mirrors with electric 

 fans, during the exposures with the spectroheliograph, to prevent distortion 

 and change of focal length. 



