REPORT OF THE SECRETARY. 27 



ASTROPHYSICAL OBSERVATOEY. 



The operations of the Astrophysical Observatory have consisted 

 chiefly in experiments in the holographic analysis of the inira-red solar 

 spectrum and the preparation of a report thereon, which was completed 

 in May of the present year, and contains, in addition to introductory, 

 historical, descriptive, and theoretical matter and accounts of subsidiary 

 investigations, tables of positions of 222 absorption lines in the infra- 

 red solar spectrum in terms of angular deviations and refractive indices 

 for arock-salt prism, and of the approximate wave-lengths corresponding. 



These results are based on observations taken between October, 1896, 

 and January, 1897, which are far superior to any before obtained, by 

 reason of the great improvements in iustrumental equipment spoken 

 of in my last report. In this research it has thus been necessary to 

 bestow what may seem inordinate time on the production of preliminary 

 results chiefly useful in indicating requisite refinements of apparatus 

 and of method. This once done, the results to be obtained in a few 

 months exceed in value, for the main purpose of the investigation, all 

 that have been obtained in as many years. An examination of the 

 earlier holographs has, however, recently been undertaken, and a great 

 number of measurements made on the relative amounts of energy in 

 the various parts of the spectrum, which, it is hoped, will lead to inter- 

 esting results when compared with weather records covering the same 

 interval of time. 



A more detailed account of the work of the Observatory will be 

 found in the appendix. Itisregretted that owing to unforeseen delays, 

 not in any way due to the Observatory, the rej)ort above mentioned is 

 not yet in type, so that the results obtained, which it is believed will 

 be a. contribution of interest and value to physical science, are not yet 

 generally accessible. I trust that the obstacle preventing publication 

 may be removed immediately after the assembling of Congress. 



Eespectfully submitted. 



S. P. Langley, 

 Secretary of the Smithsonian Institution. 



