46 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



is lost in stray light somewhere below C. But from B 2 to B 3 is a 

 period of 20 minutes, during which there were 2}4 complete rotations 

 (5 swings) of the shutter, and the apparatus rose about 3,000 meters. 

 Apart from the slight fall of temperature shown at B 2 , when the 

 instrument was removed from the balloon shed, there is no appreciable 

 sudden change of temperature, but only the gradual march attending 

 increasing altitude. No periodic change attributable to the opening 

 and closing of the shutter is discernible. From this we conclude that 

 no considerable error is caused by the current of air due to the uprush 

 of the balloons, which it was thought might cool the disk unequally, 

 depending on whether the shutter is open or not. 



2. THE DAY RECORD 



The record obtained in the day flight of July n, 1914, was on solio 

 paper. It was read up while still unfixed, and was at that time very 



Fig. 9. — Balloon Pyrheliometer Record, July 11, 1914. (From a Tracing.) 



clear and good. Unfortunately it was submitted to the process of 

 toning, without being first photographed, and became so faint that it 

 is quite impossible to reproduce it, although it is still readable. 



