NO. 4 SOLAR RADIATION ABBOT, FOWLE, AND ALDRICH 



While the effect of the downward current of 

 air seems to be nearly negligible, as indicated 

 above, it may be possible that the considerable 

 difference of temperature between the disk and 

 the air during recording at highest altitudes 

 tended to alter or change the sign of this error. 



In consideration of all circumstances, it 

 seems to us that the various small positive 

 corrections, including the error below men- 

 tioned in determining the angle of the cone of 

 rotation, but not that for clock rate or for in- 

 clination, may be regarded as balancing the va- 

 rious small negative corrections. We consider, 

 therefore, in what follows, only the direct 

 results of the exposures, the calibration at 

 Washington, the correction for effective solar 

 zenith distance, the correction to mean solar 

 distance, the correction for clock rate, and the 

 probable correction to reduce to outside the 

 atmosphere. 



CIRCUMSTANCES OF OBSERVATION 



The following circumstances attended the 

 balloon pyrheliometer nights at Omaha : Ob- 

 servers : For the Smithsonian Institution, L. B. 

 Aldrich; for the U. S. Weather Bureau, Dr. 

 Wm. R. Blair, B. J. Sherry, and Mr. Morris. 



India rubber balloons, imported by the 

 Smithsonian Institution from Russia in July, 

 1913, were used. They were 1.25 meters in 

 diameter, inflated with hydrogen gas, and were 

 sent up in groups of three attached as shown 

 in figure 7. 



It was expected that after two of the bal- 

 loons had burst by expansion, at high altitudes, 

 the third would bring down the apparatus in 

 safety. A reward was offered for the safe 

 return of the apparatus by the finder. 



In addition to the barometric element, as a 

 means of measuring heights reached, the bal- 

 loons were observed by two theodolites, sepa- 

 rated by a known base line. 



Fig. 7. — Method of 

 Suspending Balloon 

 Pyrheliometer. 



