88 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
forecasting. Third, investigations at Calama based upon the obser- 
vations there indicated a new empirical method of determining the 
solar constant of radiation, which appears to be equally as accurate 
as the old and to have the great advantages: (1) That it avoids the 
assumption of uniformity of atmospheric transparency during the 
several hours formerly required for observing, and (2) that it di- 
minishes the time required for computing the result from about 15 
hours to about 3 hours. 
PERSONNEL. 
Miss Florence A. Graves, computer, was placed on furlough be- 
ginning September 5, 1918, in order that she might take up work in 
connection with the Red Cross operations in France. 
Miss Gladys L. Thurlby reported as assistant computer on Decem- 
ber 2, 1918, and Miss Inez A. Ensign reported as computer on Feb- 
ruary 1, 1919. 
SUMMARY. 
At Washington, outside of the usual reductions of observations and 
various pieces of experimental investigation, some connected with 
the war, others with the study of radiation, but for which, for one 
reason or another, no definite result can at present be reported, 
progress has been made with the preparation of a new optical me- 
dium, potassium iodide, for the investigation of the rays beyond 
where rock salt is transmissible, and a new instrument based upon the 
principle of the perfect radiator or “absolutely black body” has been 
prepared and is undergoing test for the purpose of measuring noc- 
turnal radiation such as the earth sends out to space. 
At Mount Wilson the measurements of the solar constant of radia- 
tion have been continued, and a very neat and excellent piece of 
work has been done by Mr. Aldrich, in cooperation with the Army 
Balloon Schcol at Arcadia, on the measurement of the reflection of 
sun and sky radiation from great sheets of clouds, which lead to the 
result that a fully clouded earth would reflect to space 78. per cent of 
the radiation of the sun falling upon it. 
In South America, a successful expedition by Dr. Abbot observed 
the total eclipse of the sun on May 29 at La Paz, Bolivia. .Good 
photographs of the phenomenon and also pyranometric observations 
by Mr. A. F. Moore of the brightness of the sky were obtained dur- 
ing the progress of the eclipse. A conference which is likely to prove 
of great future value was held by Dr. Abbot with the chief and chief 
forecaster of the Argentine meteorological service with reference to 
the employment of solar radiation measurements for weather fore- 
casting. At Calama, Chile, Dr. Abbot, in cooperation with the 
Smithsonian observers there, Messrs. Moore and Abbot, devised a 
