591' TRANSACTIONS OF SECTION A. 



(ii) The Warm Sfraf, t n in the Afmo.'phere at Heights exceeding Bight 

 Miles in the Unita I states. By Professor A. Lawrexce Rotcr. 



The only ballons-sondes t'lat have been used in America are those launched 

 by the author. Sincu his obFervatory at Bhie Hill lies too near the coast for 

 the purpose, most of the balloons have been despatched from St. Louis, Missouri. 

 The experiments were begun in September 1904, and have been continued bince 

 that time, duringdirt'erent seasons, with the aid of grants from the Smithsonian 

 Institution. Of the seventy-six balloons sent up from St. Louis, all but four 

 have been found and returned, the majority falling within a radius of two 

 hundred or three hundred miles to the eastward of St. Louis. The balloons are 

 of rubber, the instruments of Teisserenc de Bort's construction, calibrated for low 

 pressures and temperatures before each ascension, and all ascensions were made 

 after sunset, to avoid the effect of solar radiation. 



Most of the balloons which rose higher than eight miles (12,870 metres) 

 entered the warm stratum, whose temperature continued to increase with 

 increasing height. The stratum was at its lowest level in summer, with a mean 

 minimum temperature of — 54°'6 C. at 12,000 metres. During the autumn of 

 1907 the warm stratum was penetrated eight times, the mean minimum tempera- 

 ture of — 60°'5 C. occurring at 12,370 metres. The variations in height from day 

 to day were large, a minimum temperature of — G7°'l C. at a height of 14,500 

 metres on October 8 being followed, two days later, by a descent of the minimum 

 temperature of — 62°'2 0. to 12,000 metres. The temperatures at the extreme 

 heights reached were —58° C. at 16,500 metres on October 8 and —56° 0. at 

 lo,0'J0 metres on October 10, showing an increase of 9° C. in 2,000 metres and 

 — 6°-2 in 4,500 metres respectivelv. On November 6 the minimum temperature 

 of -52°-2C. was found at 9,700 "metres, and -50°-5 C. at 10,000 metres, the 

 highest point attained. On November 8 the level of the minimum of — 63°'l C. 

 had risen to 14,250 metres, with an increase of temperature to — 60°-2 C. at 

 15,380 metres. These observations are to be published in e.vtenso and discussed 

 in the ' Annals of the Astronomical Observatory of Harvard College,' under the 

 author's direction. 



These results, which were made near 35° North latitude, show the warm 

 stratum to be at a decidedly higher altitude than it is in northern Europe. On 

 the contrary, the results obtained by the expedition which was sent jointly by 

 M. Teisserenc de Bort and the author in 1906-7 to explore the atmosphere over the 

 tropical Atlantic indicated a still higher level for the warm stratum. In fact at 

 the height of 15,000 metres over the equator there was no inversion of tempera- 

 ture, and it was actually colder than at an equal height in the northern latitudes. 



2. Report on the Measurement of the Geodetic Arc in Africa. 

 See Reports, p. 56. 



3. Seventh Reqyort on the Investigation of the Upper Atmosphere by moans 

 of Kites. — See Reports, p. 59. 



4:. Report on the Magnetic Observations at Falmouth Observatory. 



See Reports, p. 55. 



5. Report of the Committee on Electrical Standards. — See Reports, p. 31. 



6. Report on Meteorological Observations on Ben Nevis. — See Reports, p. 58. 



