152 proceedings: philosophical society 



The 766th meeting was held on January 22, 1916, at the Cosmos 

 Club. President Briggs in the chair, 51 persons present. The min- 

 utes of the 765th meeting were read in abstract, corrected, and 

 approved. 



REGULAR PROGRAM 



Mr. C. G. Abbot presented a paper entitled, New proofs of the solar 

 variability. The Smithsonian Astrophysical Observatory has inves- 

 tigated for 12 years the intensity of solar radiation. In speaking of 

 the variability of the sun we do not refer to variations caused by the 

 atmosphere of the earth or by the yearly fluctuations of the earth's 

 solar distance. The latter are readily eliminated. The elimination of 

 atmospheric influences depends on spectrobolometric observations at 

 different altitudes of the sun, reduced in accordance with sound theory. 

 Experiments at Washington, Mount Wilson, Mount Whitney, and Bas- 

 sour (Algeria), under circumstances differing widely as to atmospheric 

 temperature, pressure, humidity, and length of path, are in close 

 agreement in their indications of the intensity of solar radiation out- 

 side the atmosphere. The results are further checked by confirmatory 

 observations at different altitudes ranging on the earth from sea-level 

 to Mount Whitney, and by manned balloons to 8000 meters, and by 

 sounding balloons to 25,000 meters. Variations of solar emission of 

 radiation were indicated by Mount Wilson observations and confirmed 

 by simultaneous work at Bassour, Algeria. A correlation coefficient of 

 50=*= 7 per cent is found between the variations noted at the two sta- 

 tions. This leaves the chance of accidental correlation 1 in 25,000. 

 Four years of pyrheliometry at the Arequipa, Peru, station of the 

 Harvard College Observatory, under direction of Professor E. C. 

 Pickering, are now being published by the Smithsonian Institution. 

 This work confirms the solar variability from day to day, and from 

 year to year, found at Mount Wilson. Measurements of the distri- 

 bution of radiation along the diameter of the solar image have been 

 made by the Smithsonian observers at Washington and at Mount 

 Wilson. Fluctuations of contrast between the center and the edge 

 of the sun are found to occur in all wave-lengths, but greater for short 

 wave-lengths than for longer ones. These fluctuations occur from day 

 to day and from year to year. Both kinds of changes are correlated 

 in time with changes in solar radiation. Curiously the correlation is in 

 opposite senses for long-period and short-period changes. When 

 great solar activity prevails, as shown by sun-spots, faculac, etc., high 

 solar-radiation values predominate, and a greater contrast of bright- 

 ness between the center and the edge of the sun is found. But when 

 irregular changes of the solar radiation occur in the short period, they 

 are associated with less contrast of brightness between the center and 

 the edge of the sun. The first type of change was explained as a tem- 

 perature effect, the second as due to changes of transparency of the 

 outer solar envelope. The paper was illustrated by lantern slides. 



Discussion: Mr. Swann pointed out that some of the data deter- 

 mined from variation in the sun's atmosphere were suggestive of solec- 



