112 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



the balloons is similar to that already found. (See Bulletin Mount Weather 

 Observatory, Washington, 191 1, 4: 186.) It indicates that, in addition to the 

 known factors entering into the ascensional rate of any balloon, there is the 

 unknown factor of the difference in temperature between the gas in the balloon 

 and the air through which the balloon is passing. While the temperature 

 distribution in the free air is in general known, it would be impossible to 

 predict, with sufficient accuracy for a particular ascension, the point of maxi-. 

 mum ascensional rate or minor variations in the rate. On the other hand, 

 careful observation of the ascensional rate of a free, sealed, rubber balloon 

 might indicate fairly well the peculiarities of the temperature distribution at 

 the time of the ascension. In this connection the author calls attention to an 

 entirely erroneous statement in Bulletin of the Mount Weather Observatory, 

 4:186, regarding the adiabatic cooling of hydrogen gas. The approximate 

 rate of cooling per kilometer came in some way to be considered the rate to 

 the 15-kilometer level. The statement based on this error should not have 

 appeared, nor is it needed to account for the observed peculiarities in the 

 ascensional rate of free rubber balloons under consideration. 



The instruments used were the same as those used in prevkms series of 

 soundings. The calibration of the instruments was similar to that for pre- 

 vious series, except that the pressure and temperature elements were calibrated 

 in a smaller chamber in which ventilation and temperature were under some- 

 what better control and in which temperatures down to — 6o° C. could easily 

 be obtained. (See Bulletin Mount Weather Observatory, Washington, 191 1, 

 4:187.) 



The data obtained in each ascension are presented in table 4 with inter- 

 polations at the 500-meter intervals up to 5 kilometers above sea level, and at 

 i-kilometer intervals above the 5-kilometer level. In figure 4 a diagram of 

 the temperature-altitude relation is shown for each observation. Figure 5 

 shows the mean value of this relation for the period. The free air isotherms 

 for the period are shown in figure 6. The horizontal projections of the 

 balloon paths, as far as they could be observed, are shown in figure 7. Only 

 one theodolite was used, the altitudes being computed from the observed 

 air pressures. 



An inversion of temperature, with the maximum temperature somewhere 

 between the Y?- and 2-kilometer levels, is shown in each curve of figure 4. 

 This inversion of temperature is found, whether the observation be made in 

 the morning, near noon, or in the late afternoon. It does not seem to accom- 

 pany any particular wind direction. A similar inversion of temperature was 

 observed in most of the ascensions made at Indianapolis, Fort Omaha, and 

 Huron. 



As shown in figure 5, the altitude at which the mean temperature for the 

 period is a minimum is 17 kilometers. The minimum temperature observed 

 in any ascension may be more than a kilometer above or below the height of 

 this mean. In two ascensions, those of the 23d and 27th of July, the change 

 of temperature with altitude begins to decrease at about the 8-kilometer level, 

 while in the ascensions of August 2 and 3 this change does not take place 

 until the 12-kilometer level. The temperature change from day to day is best 

 shown in figure 6. The lowest temperature observed, — 67.5° C, was at about 

 the 16.5-kilometer level on August 3. About the same temperature had been 

 observed at the 16-kilometer level on the day before. 



