156 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



miles roached or exceeded. The mechanical equipment used in kite 

 fl3'inf:: has hcon hrouf^ht to a high state of perfection, as evidenced by 

 the few "bn>akaways" of the kites during the year, but a kite 

 meteorograph satisfactory in all respects remains to be constructed. 



The classilication and compilation of the Mount Weather kite and 

 balloon (^ata necessary in order to study Ihe information secured 

 under dillerent weather conditions have been a part of the office work 

 during the year, and a summary of the mean results for three years 

 has been prepared and is now in the hands of the printer. It will 

 appear as part 2, Volimie IV, of the Mount Weather Bulletin. 



A most important piece of work was accomplished by the Mount 

 Weather Observatory during the year in the completion of two 

 sounding-balloon campaigns, the first at Huron, S. Dak., and the 

 second at Fort Omaha, Nebr. Some account of the earlier work in 

 this direction was given in my last annual report. In order to 

 present the subject intelligently, I shall repeat some of the facts 

 given in previous reports. 



The use of small free balloons to carry meteorological instruments 

 into the upper regions of the atmosphere dates from 1893, nearly 20 

 years ago, when Messrs. Hermite and Besangon in France sent up 

 varnished paper balloons carrjnng registering instruments whicn 

 brought back a record of the meteorological conditions encountered 

 in the ascension. To Assman, of Germany, however, is due the sub- 

 stitution of small rubber balloons in these ascents. The expansion 

 of the confined gas at great altitudes bursts the balloon, the landing 

 of the instrument being effected by means of a light parachute with 

 which the balloon is covered. 



The first series of sounding-balloon ascents in the United States 

 was made at St. Louis, Mo., in the years 1904 to 1907, inclusive, 

 under the direction of Prof. A. Lawrence Rotch, of Blue Hill Observ- 

 atory. Prof. Rotch conducted 77 ascensions, the instruments bemg 

 recovered in all but 5 cases. Thirty-seven of the ascensions reached 

 an altitude of 10,000 meters (6 miles) or greater. In the series by 

 Prof. Rotch heights exceeding 10 miles (16 kilometers) were attained 

 5 times. The Mount Weather Observatory has sent up 91 sounding 

 balloons, of which number 81 were recovered. Heights exceeding 10 

 miles were attained in 37 cases, the greatest height attained being 

 18.9 miles at Huron, S. Dak., on September 1, 1910. 



The exploration of the atmosphere by means of sounding balloons 

 has become an international work and is carried on through an inter- 

 national commission of which Prof. H. Hergesell, of Strassburg, is 

 president. Through this commission are collected and published the 

 results of aerial observations made quite generally at appointed times 

 by aU meteorological services in the Northern Hemisphere. The most 

 important single result that has come from the observations is the 

 discovery of a region in the atmosphere, about 7 miles above the 

 earth's surface, where the fall in temperature with increasing altitude 

 ceases. On the contrary, there may be a slight rise in temperature 

 on entrance to this region. Although various names have been 

 assigned to this region, none fully describes its characteristics. In 

 this report it will be referred to as the "upper inversion." Inversions 

 of temperature are frequently found in the atmosphere next to the 

 earth, but they are generally small in amount and fleeting in char- 

 acter. The upper inversion, however, appears to be a world-wide 



