WEATHER BUEEAU. 75 



The pyi'heliometric measurements now obtained at the American 

 University are considered a continuation of similar measurements 

 made at the central office of the Weather Bureau previous to May, 

 1912. At the university the elevation of the pyrheliometers above 

 sea level is about 100 meters greater and the pollution of the atmos- 

 phere due to city conditions is considerably less than at the Weather 

 Bureau. It may be partly on this account that radiation intensities 

 in excess of any heretofore observed at Washington have been 

 measured at the university during the past year. On December 26, 

 1914, with the sun at zenith distance 62.5°, an intensity of 1.48 cal- 

 ories per minute per square centimeter of normal surface was meas- 

 ured, while on February 28, 1915, with the sun at zenith distance 

 57.5°, the intensity was 1.50 calories. 



During March and April, 1915, the stations at Madison, Wis., Lin- 

 coln, Nebr., and vSanta Fe, N. Mex., were visited by the official in 

 charge of solar-radiation investigations, and the Marvin pyrhelio- 

 meters in use were recompared with a Smithsonian silver disk pyr- 

 heliometer. The radiation measurements obtained at these stations 

 have since been tabulated in form for publication. Those for Santa 

 Fe, which is 7,000 feet above sea level and in an arid region, show 

 radiation intensities a few per cent in excess of the measurements 

 obtained at other stations. On November 20, 1914, a maxmium of 

 1.64 calories per minute per square centimeter of normal surface was 

 measured with the sun at zenith distance 55°. On the same day 

 with the sun at zenith distance 60° the intensitj^ was 1.60 calories. 

 These exceed any previous measurements obtained at Santa Fe. 

 Likewise, at Madison, Wis., the monthly maxima from November, 

 1914, to March, 1915, exceed the maxima for corresponding months 

 since the fall and winter of 1911-12, and the midday mtensity of 1.50 

 calories obtained at Mount Weather on September 28, 1914, was the 

 highest ever measured at that station. We are therefore led to the 

 conclusion that unusually clear skies were experienced in the United 

 States during the fall and winter of 1914-15, although in some dis- 

 tricts the cloudiness was above normal. 



The official in charge of sola.r radiation investigations and an 

 assistant spent most of the month of May, 1915, among the moun- 

 tains of southwestern North Caroluia, where special temperature 

 investigations in the interest of horticulture are in progress. Meas- 

 urements were made of the rate at which heat is radiated to the atmos- 

 phere from a blackened surface when located in a valley at the foot 

 of a mountam slope, when on a mountain slope, and also when on a 

 mountain peak. The results of these observations, when fully dis- 

 cussed, will be published in the Monthly Weather Review or else- 

 where. 



At the end of June, 1915, the Marvin pyrheliometer in use at Lin- 

 coln, Nebr., was moved from the Weather Bureau office, in the busi- 

 ness section of the city, to the experiment station buildmg on the 

 State University farm", just outside the city limits. A Callendar 

 pyrheliometer was also installed on the roof of the same building, at 

 an elevation of 56 feet above ground and 1,340 feet above sea level. 

 The radiation records wiU be utilized by the Nebraska experiinent 

 station in its investigations, as well as by the Weather Bureau in its 

 climatological studies. 



