116 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 192 8 



telegi'aphed values of the solar constant of radiation are being regu- 

 larly published on the "Washington daily weather map. 



As tentatively and privately forecasted in November, 1927, on the 

 basis of hitherto observed periodicities in solar phenomena, the 

 " solar constant " values reached a high level in the spring months 

 of 1928, and were expected to reach a low level in the autumn.^ 

 Much interest attaches to these tentative forecasts of the solar energy 

 to be expected for long periods in advance, but several j-ears must 

 yet elapse before (if ever) they can be made with sufficient confidence 

 to justify publication. 



Although the solar radiation measurements have been reduced to 

 a routine for several 3'ears at all our stations, the very high degree 

 of accuracy now demanded and generally achieved is occasionally 

 marred by new and unexpected accidents and difficulties. Thus 

 internal evidence disclosed that some obscure error of very consid- 

 erable amount began in August, 1927, to affect the sky radiation 

 measurements of the pyranometer on Table Mountain. Our best 

 thought and many experiments had failed to disclose the obscure 

 cause up to the close of the period of this report, but by anticipation 

 I may say that at this time of writing (October 3) the error has been 

 detected, cured, and a beginning has been made to eliminate its 

 influence from the final results of the observations. This circum- 

 stance has prevented us from making public Table Mountain results 

 hitherto. 



(&) Measurements of atmospheric ozone. — Doctor Dobson, of Ox- 

 ford, England, having perfected a spectroscopic method for deter- 

 mining the quantity of atmospheric ozone, has found that quantity 

 variable in most interesting relations to solar phenomena and to 

 weather. He has established a chain of cooperating observatories in 

 Europe, and, by aid of a grant from Mr. John A. Koebling, the 

 Smithsonian was able to equip the Montezuma station with the 

 necessary apparatus. For about one year daily measurements were 

 made at Montezuma by Field Director Freeman, aided by Mrs. Free- 

 man. The photographs taken were reduced in England by Doctor 

 Dobson and his colleagues, but, contrary to European experience, 

 showed almost zero variation. They also showed a much smaller 

 quantity of atmospheric ozone at Montezuma than in Europe. 



Finding further observations at Montezuma unnecessary because 

 of the uniformly constant results, the apparatus was returned to 

 Oxford, restandardized, and sent to Table Mountain, Calif., where it 

 is now installed for daily observing. 



(c) Expeditions to Mount Wilson. — As stated in last year's report, 

 the writer undertook at Mount Wilson, in the autumn of 1927, to 



»At this writing (October 3), this latter forecast also has been supported by September 

 results. 



