REPORT OF THE SECRETARY 



105 



on the ozone problem in that spectral roi^-ion, but also the extraordi- 

 nary relations of the ultra-violet rays to human, animal, and plant 

 physiology are coming increasingly to the fore. Our own studies 

 indicate that the solar variations are far greater for those rays than 

 they are for the solar rays as a whole. Thus the accompanying fig- 

 ure indicates that when the solar constant of radiation changes by 

 1 per cent it means almost imperceptible change for the infra-red 

 rays, but as much as 10 per cent or more for some rays of the ultra- 

 violet. 



In addition to the work at Mount Wilson on the solar cooker and 

 the ozone of the higher atmosphere, much attention was paid to 



PHisMATic pnn' 



D€\/IATION CIL/U 



Solar variation localized in the violet and ultra-violet 



attempts to improve the radiometer and the stellar-spectrum appa- 

 ratus, in the hope of going much further in studying the energy 

 spectra of the stars. Much knowledge was gained which will be 

 useful later on, and star-spectrum observations were made on sev- 

 eral nights, but no actually completed advance in stellar spectra 

 was attained. The way, however, is very clear now for future 

 advance. 



PERSONNEL 



Mr. H. B. Freeman accepted service on the private Smithsonian 

 roll as assistant at Harqua Hala in September, 1924, and succeeded 

 Mr. L. B. Aldrich in charge at Montezuma on March 1, 1925. Mr. 

 Aldrich returned to Washington. 



