POSTSCRIPT 



Our researches described above were finished during the winter 

 1916-1917, and our report was published by the Society of Science 

 in Christiania/ Since that time we have received from Dr. C. G. 

 Abbot several papers that are of the greatest importance for our 

 investigations. We may especially mention " On the Distribution 

 of Radiation over the Sun's Disk and New Evidences of the Solar 

 Variability" by C. G. Abbot, F. E. Fowle, and L. B. Aldrich 

 [1916] ; " Arequipa Pyrheliometry " by C. G. Abbot [1916] ; "The 

 Sun and the Weather" by C. G. Abbot [1917] ; "Effect of Short 

 Period Variations of Solar Radiation on the Earth's Atmosphere " 

 by H. Helm Clayton [1917]. From Dr. L. A. Bauer we have also 

 received two interesting papers : " The Local Magnetic Constant 

 and its Variations" [1914] and "Solar Radiation and Terrestrial 

 Magnetism" [1915]. 



By the various investigations described in these papers it is now 

 established beyond doubt that on the one side the radiation of heat 

 from the sun varies not only from year to year more or less periodic- 

 ally in a similar way as the sun spots, but there are also very great 

 fluctuations in the radiation within short intervals of a few days, and 

 on the other side it is shown that correlations exist between these 

 fluctuations in the solar radiation and meteorological and magnetic 

 changes on the earth. 



INVESTIGATIONS ON FLUCTUATIONS IN SOLAR RADIATION 

 BY ABBOT, FOWLE, AND ALDRICH 



In their paper : " On the Distribution of Radiation over the Sun's 

 Disk " (by C. G. Abbot, F. E. Fowle, and L. B. Aldrich) the authors 

 prove that there is a great, difference in the distribution over the 

 sun's disk of the various solar rays. The contrast of brightness 

 between the center and the edge of the sun is greatest for short 

 wave lengths and diminishes as one comes to the red and infra-red. 

 " There are, however, slight but significant differences between the 

 mean results of different years,'* greater contrast of brightness 



* Skrifter utgit av Videnskapsselskapet i Kristiania 1916. I Mateni. — Xa- 

 turv. Klasse. Vol. I, No. 9. Kristiania, 1917. 



267 lir. 



