52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



the two balloons were observed to burst. Accordingly while no 

 suspicion attaches to the record at maximum elevation, it is worthless 

 at intermediate elevations. 



The barometer element was calibrated by enclosure of the whole 

 instrument in a brass box from which air could be exhausted, and of 

 which the temperature was regulated by immersion in a stirred bath 

 of gasoline cooled by expansion of liquid carbon dioxide. In one set 

 of experiments the sensitiveness of the element to change of pressure 

 was determined at several constant temperatures ranging from +34 

 C. to — 49 C, and the change of zero with change of temperature 

 was determined as a correction. In another set of experiments, both 

 temperature and pressure were simultaneously lowered to correspond 

 with the temperatures and pressures indicated by the foregoing 

 results of the Weather Bureau observers. 



We assume that at the time of launching" at Omaha, the instrument, 

 being shone upon by the sun, was 5° in excess of the air temperature, 

 and hence at +34 C. We assume that at the maximum elevation 

 the instrument was at — 37 C. 



From experiments of December 26, 19 14, and February 1 and 4, 

 1915, we find that the zero of the barometric element changed linearly 

 at the rate of 0.123 mm. per degree, in the sense to diminish the 

 barometric deflection attending falling pressure. Hence for a fall 

 of 71 ° the correction is 8.7 mm. 



From the record of July 11, 1914, the barometric deflection is 

 37.8 mm. at highest altitude. Corrected deflection, 46.5 mm. From 

 numerous experiments at various constant temperatures, 76.4 cm. 

 mercury pressure corresponds to a deflection on our record of 

 50.3 mm. Hence for July 11, 1914, the change of pressure was 



=!— ^ X 76.4 = 70.7 cm. Hg. The barometer reading at Fort Omaha 



was 73.33 cm. Hence, by these experiments, the pressure at maxi- 

 mum elevation was 2.63 cm. Hg. 



Again, on March 18, 1915, a change of pressure of 72.3 cm. Hg., 

 and accompanying change of temperature from +34.8 to — 30 , 1 

 gave a barometric deflection of 40.0 mm. Hence, from +34 to 

 — 37 would have given a deflection of 39.1 mm. Hence, the change 



of pressure on July 11 was ^Zi_ X 7 2 -3 = 700. 



Hence, by these experiments the pressure at maximum elevation 

 was 3.33 cm. Hg. As a mean result, we decide that at maximum 



1 Here the carbon dioxide used for cooling purposes was exhausted. 



