350 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ber, 1904. During that month four ascensions were made, all the bal- 

 loons falling about 50 miles east of St. Louis within a distance of 15 miles 

 of one another, and at the maximum height of ten and a half miles a 

 temperature of — 62° F. was recorded. Another series of 10 ascensions 

 was made during the closing days of the Exposition in the latter part of 

 November and the first days of December, mostly after sunset to avoid 

 the possible effects of insolation. Owing to the stronger air currents at 

 this season, two of these balloons travelled with a mean velocity of more 

 than one hundred miles an hour and all hut one fell within the eastern 

 half of a circle having St. Louis as its centre and a radius of 280 

 miles. The exception was a balloon which did not rise above the surface 

 wind. In general the drift was away from the areas of low barometric 

 pressure at the ground, thus confirming the theory of the outflow of air 

 above them. An extreme height of almost ten miles was attained, and a 

 temperature of —76° F. was found once somewhat below seven miles. 



In order to continue these observations during the winter, the author 

 executed at his own expense another series of nine ascensions during the 

 latter part of January and on the days of the international ascensions 

 abroad in February and March, respectively. The gas required was 

 generated in barrels by the acid process. One of these balloons was 

 lost, but the others fell nearly within the semi-circle described above. 

 Several of the records are incomplete, owing to stoppage of the clock 

 movements, and another was obliterated by the finder, but a height ex- 

 ceeding ten miles was indicated, and the extraordinarily low temperature 

 of — 111° F. was registered at the height of about nine miles during the 

 prevalence of a high barometric pressure at the ground. Most of the 

 ascensions were conducted by Messrs. Clayton and Fergusson of the Blue 

 Hill Observatory staff, and it is due to their skill and perseverance in 

 overcoming difficulties, consecjuent on undertaking a new work away 

 from home, that such good results were obtained. The records have 

 been partially reduced by Mr. Clayton and a summary of them is given 

 in the accompanying table, but the temperatures and heights must still 

 be regarded as more or less approximate. A complete publication will 

 be made with the investigations of the Blue Hill Observatory in the 

 " Annals of the Astronomical Observatory of Harvard College." 



The annual variation of the temperature at great heights in the free 

 air above the American continent is not yet known, and to ascertain this 

 the writer will undertake a fourth series of observations with registra- 

 tion balloons this summer at St. Louis, the expense being met by a 

 grant of $1,000 from the Hodgkins Fund held by the Smithsonian In- 

 stitution to aid research relating to the atmosphere. 



