90 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



mass one reading of the crossing point of the wire over the fixed 

 scale gives the intensity as it ^yould be outside the atmosphere, and a 

 second reading on the movable scale gives the atmosphere transmis- 

 sion coefficient. No logarithms or computing are required. 



The equipment of the expedition was all boxed ready for ship- 

 ment to South America when circumstances connected with the war 

 with Germany led to a postponement. Under these circumstances it 

 was deemed best to send the expedition to Hump Mountain in North 

 Carolina, a station at 4,800 feet elevation, where it is now located. 

 This location was chosen with a view to its being at a great distance 

 from Mount Wilson, in a region where Weather Bureau observers 

 reported uncommonly little cloudiness, and easily accessible from 

 the railroad and from Washington. 



The expedition with over 3 tons of equipment went forward in 

 May, 1917. It is in charge of Mr. A. F. Moore, who is assisted by 

 Mr. L. H. Abbot. Two small frame buildings were erected for the 

 observing and living quarters. The apparatus was set up and ad- 

 justed by Messrs. C. G. Abbot, L. B. Aldrich, and A. F. Moore, and 

 gotten ready for observing about June 15. Unfortunately the most 

 cloudy and rainy summer in the recollection of old residents had 

 been experienced up to August 1. Otherwise, everything is highly 

 favorable to excellent solar-constant work. If war conditions war- 

 rant, the Institution still hopes to send the expedition to South 

 America later, where a station is selected at which 300 cloudless 

 forenoons for observing per year are to be expected. 



Before leaving this subject I desire to call attention to the remark- 

 able paper by Dr. Helm Clayton (Smithsonian Misc. Coll., vol. 

 68, No. 3) on the " Effect of Short Period Variations of Solar Eadia- 

 tion on the Earth's Atmosphere." Doctor Clayton shows by the mathe- 

 matical method of correlations, free from all influence of personal 

 judgment, that variations of solar radiation observed by us at Mount 

 Wilson in 1913 and 1914 were reflected in variations of terrestrial 

 temperatures all over the world. The correlations were positive in 

 and near the Tropics, negative in Temperate Zones, and positive near 

 the poles. A lag of from 1 to 5 days occurred, the lag being less for 

 Tropical Zones. The barometric pressure also appeared to join in 

 the correlations. By an ingenious application of his method Doctor 

 Clayton shows that the short interval fluctuations of solar radiation 

 are not altogether without periodicity, for the changes tend to repeat 

 themselves after 11 and 22 days, respectively. The same tendency is 

 found in the temperature records of Buenos Aires. We are now en- 

 gaged in testing this conclusion by computations for other years. 



Computations of Mount Wilson solar observations went on in the 

 hands of Miss Graves as usual at Washington, and the computing is 

 practically uj) to date. 



