14 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



was possible to maintain the initial temperature constant, within one- 

 third of a degree, at any desired point between +20° and —120°, and 

 the final temperature similarly constant between +20° and the tem- 

 perature of liquefaction. The temperatures were measured by resist- 

 ance thermometers placed close to the valves in the high and low 

 pressure circuits. The pressures employed range from 500 pounds to 

 3,000 pounds. The expansion was exclusively to one atmosphere. 



The inquiry is of interest as related to the functioning of air 

 liquefiers in which the air is throttled by a valve and expands without 

 performing external work, in the usual sense of that expression. 



STUDY OF THE UPPER ATMOSPHERE. 



A further grant from the Hodgkins fund was made to Prof. A. 

 Lawrence Rotch, director of the Blue Hill Meteorological Observa- 

 torj, to aid in the completion of his experiments with ballons-sondes 

 at St. Louis. This was accomplished in October and November, 1907, 

 under the direction of Mr. S. P. Fergusson. 



The object of these latest ascensions, 21 in number, was to supply 

 data for the high atmosphere during the autumn, a season when 

 there are few observations, and also to establish a comparison with 

 the results obtained simultaneously in Europe on the international 

 term days in October and November. Professor Rotch reports that 

 all but two of the instruments used in these ascensions were recov- 

 ered, and an examination of the record sheets indicates generally the 

 presence, at an altitude exceeding 8 miles, of the isothermal, or rela- 

 tively warm stratum, which was found somewhat lower in summer. 

 For example, on October 8 the minimum temperature of 90° F. below 

 zero was found at a height of 4T,G00 feet, whereas at the extreme alti- 

 tude reached — namely, 54,100 feet — the temperature had risen to 72° 

 F. below zero. Similarly, on October 10 the lowest temperature of 

 80° F. below zero occurred at 39,700 feet, while 69° F. below zero was 

 recorded at 49,200 feet, the limit of this ascension, showing that the 

 temperature inversion had come down about 8,000 feet in two days. 



The prevailing drift of the balloons during the autumn of 1907 was 

 from the northwest, while in })revious years they traveled more from 

 the west. A description of the methods employed in launching 77 

 ballons-sondes from St. Louis and a discussion of the results obtained 

 will soon appear in the Annals of the Astronomical Observatory of 

 Harvard College. 



AIR SACS OF THE PIGEON. 



For several years there have been in progress under the general 

 direction of Prof, von Lendenfeld, of the University of Prague, aided 

 V)y grants from the Hodgkins fund, various investigations bearing 

 upon animal flight. The results of one of these investigations, on 



