204 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Miss Sheldon has divided her time between work relating to the physical 

 laboratory, to solar spectra, and to photographic photometry. Of the plates 

 measured, 52 are of laboratory spectra and 89 relate to photometry. The 

 remainder, including a large number, are of solar magnetic fields. Many 

 of these were measured in duplicate, with different measuring instruments. 

 Miss Sheldon has also determined the screw errors of several comparators 

 and has given much time to miscellaneous computations, recording, etc. 



Miss Smith has continued her work upon spectroheliograph plates. This 

 has included the determination of the areas of the calcium flocculi upon 254 

 negatives, thus completing the reductions to March 20, 1912. The curves 

 showing the fluctuations of the areas have been drawn to October 191 1. 

 Miss Smith has measured, in addition, 146 prominence plates, completing 

 the reduction of this series to January 1, 1912, and has made 496 prints of 

 negatives of calcium and hydrogen spectroheliograms. 



Miss Ware has continued during the year her measures and reductions 

 of solar and laboratory spectra obtained by Mr. St. John. These plates, 

 of which about 150 have been used, were made for the purpose of testing 

 the accuracy of the plane grating when employed for the determination of 

 standard wave-lengths, and for the derivation of the wave-lengths of ter- 

 tiary standards. The publication of the first results of this investigation has 

 been made jointly by Mr. St. John and Miss Ware. 



The library has remained in charge of Miss Haines. The accessions of 

 bound volumes during the year number 733, of which 470 were acquired by 

 purchase, 211 by binding, and 52 by gift. The total number of bound 

 volumes now in the library is 2,550. Miss Haines has also assisted with 

 the editorial work of the Observatory. 



INVESTIGATION OF THE PHOTOGRAPHIC PROCESS. 



Modern astrophysical work makes unusual and exacting demands upon 

 photography, not wholly satisfied by the plates and the methods of develop- 

 ment now available. The small light intensities active in the registration 

 of faint stars and in the photography of spectra of high dispersion require 

 plates of the highest attainable speed; the differentiation of delicate detail 

 on planetary surfaces and in nebulae and the separation of close spectral 

 lines require plates of strong contrast and fine grain ; the investigation of 

 special spectral regions, such as the infra-red, the blue-green, and the ex- 

 treme ultra-violet, for which the ordinary emulsions of the silver haloids 

 are not highly sensitive, necessitates plates specially treated with optical sen- 

 sitizers. Any improvement in any one of these particulars — speed, grain, 

 color sensitiveness — would increase correspondingly the efficiency and scope 

 of astrophysical work. One has but to consider the question of speed alone, 

 and from the single standpoint of efficiency, to appreciate the importance of 

 such improvements. With a telescope or spectrograph practically all of the 

 time that the instrument is in use may be spent in the actual exposure of 



