NO. 4 SOLAR RADIATION — ABBOT, FOWLE, AND ALDRICH 49 



UNITED STATES DEPARTMENT OF AGRICULTURE, 



Weather Bureau, 



Office of the Chief, 



Washington, D. C, March 15, 1915. 

 Dr. C. D. Walcott, 



Secretary, Smithsonian Institution, 

 Washington, D. C. 

 Dear Sir : 



Replying to your letter of March 13, 1915, no readings of pressure and 

 temperature were taken preceding the morning ascension of July 11, 1914. 

 However, a reading was taken after the ascension, at I p. m., and another just 

 preceding the second ascension, at 4 p. m. These readings were : 



Pressure Temperature 



At I p. m 732.5 mm. 32.3 C. 



At 4 p. m 732.0 mm. 33.1 C. 



The values at the Weather Bureau Station in Omaha at these hours were : 



Pressure Temperature 



At 1 p. m 730.8 mm. 35.6° C. 



At 4 p. m 730.2 mm. 35.6 C. 



Applying these differences, + 1.8 mm. for pressure and — 2.8° C. for 

 temperature, to the value at 10.30 a. m. at Omaha, viz., 731.5 mm. and 

 32.2 C, we get 733.3 mm. and 29.4 as the probable values at Fort Omaha 

 just preceding the first ascension, or 10.30 a. m. 



Very respectfully, 



C. F. Marvin, 



Chief of Bureau. 



UNITED STATES DEPARTMENT OF AGRICULTURE, 



Weather Bureau, 



Office of the Chief, 



Washington, D. C, March 9, 1915. 

 Dr. C. D. Walcott, 



Secretary, Smithsonian Institution, 

 Washington, D. C. 

 Dear Sir : 



I inclose herewith the data for July 11, 1914, requested by you in your letter 

 of January 29, 1915. They include, for the first ascension, when the balloon 

 pyrheliometer was taken up, altitudes each minute as long as the balloons could 

 be observed at both stations ; for the second ascension, in the afternoon, 

 temperatures at those levels in which the temperature-altitude relation changed, 

 and interpolated values at 500-meter levels up to 5,000 meters, and at 1,000- 

 meter levels above 5,000 meters. Pressures also are given, wherever it was 

 possible to compute them. A considerable portion of the record has been 

 rubbed off, by reason of its having lain in a mud pond for some days. There 

 were several pounds of mud in the instrument when it was received. All 

 altitudes were computed from the two-station theodolite observations. 



The ascensional rates for the two ascensions are almost identical up to 6,000 

 meters. Assuming that they continue in this relation, a curve extended for 



