4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



\J° altitude above the horizon. The rest of the day the sun was 

 red and could be observed with the unprotected eye. At the time of 

 new moon the nig-hts were so bright that the light was compared to 

 that of full moon, even at midnight. 



In 1814 occurred the great eruption of the volcano of Mayon in 

 the Philippine Islands, and on April 7 to 12, 1815 the extraordinary 

 outbreak of Tomboro, Sumbawa, of which it is said this eruption 

 was the greatest since that of Skaptar Jokull in 1783. For three 

 days there was darkness for a distance of 300 miles. After these 

 extraordinary volcanic outbreaks there were noted in Europe streaky 

 skies, haziness, long twilights and red sunsets, so that the year 18 15 

 is the most remarkable as regards sunset lights recorded up to that 

 date. 



Passing on to the year 183 1 there occurred three moderate erup- 

 tions, and three more of the very first magnitude. Thus Graham's 

 Island was thrown up. and eruptions took place in the Babujan 

 Islands and at Pichincha. Arago says " the extraordinary dry fog 

 of 1 83 1 was observed in the four quarters of the world. It was 

 remarked on the coast of Africa on August 3, at Odessa on August 

 9, in the south of France and at Paris on August 10, in the United 

 States on August 15. The light of the sun was so much dimin- 

 ished that it was possible to observe its disk all day with the unpro- 

 tected eye. On the coast of Africa the sun became visible only after 

 passing an altitude of 15 ° or 20 . M. Rozet in Algeria and others 

 in Annapolis, United States, and in the south of France, saw the 

 solar disk of an azure, greenish, or emerald color. The sky was 

 never dark at night, and even at midnight in August small print 

 could be read in Siberia, Berlin, Genoa, etc. On August 3 at 

 Berlin the sun must have been 13 below the horizon when small 

 print was legible at midnight." 



MOUNT KATMAI AND THE SOLAR RADIATION 



In the following table we give the transmission of the atmosphere 

 for the solar radiation as determined by the pyrheliometer, and for 

 the separate wave-lengths by the spectrobolometer. In the first 

 column we have the ratio of the mean values of the total intensity of 

 the solar radiation (as determined by the pyrheliometer) compared 

 with the intensity of the radiation which would be obtained outside 

 the atmosphere, on the moon, for instance. The results are grouped 

 with regard to time as indicated in the side headings. Pyrheli- 

 onieter measurements of the different davs have been reduced to the 



