1909] BY MEANS OF KITES AND BALLOONS. 11 



have been made with either kites or captive balloons, the latter being 

 used only when the wind is insufficient to support the kites, or about 

 one day in twenty. The apparatus in use at Mt. Weather is still 

 undergoing improvement. The mean height at which daily (except 

 Sunday) temperature and other observations are obtained is ap- 

 proximately 3,000 meters, or about 2 miles, above sea level. The 

 highest altitude so far attained by means of kites is 7,044 meters, 

 about 4f miles. This flight was made at Mt. Weather on October 

 3, 1907. Flights closely approximating this in height were made at 

 the same observatory on April 14 and September 30, 1908, while the 

 fourth highest record, 6,430 meters, was made by the German 

 Observatory at Lindenburg in November, 1905. 



In the same year that Hargrave invented his kite, Charles Renard 

 suggested the use by meteorolgists of small free balloons made of 

 paper or other suitable material and having sufficient lifting power 

 to carry up self-recording instruments. A balloon of this sort par- 

 tially inflated with hydrogen at the earth's surface rises until the 

 gas expands sufficiently to burst it, and the instrument is let down 

 safely from this point by means of a small parachute. 



Teisserenc de Bort, at his observatory at Trappes, Paris, and 

 from the decks of ocean steamers, has obtained upper air records of 

 great importance to meteorology with these paper balloons as well 

 as with kites. More recently Assmann introduced india-rubber 

 balloons about six feet in diameter. These are now the more gener- 

 ally used. 



Preparatory to an ascension, this balloon is filled until the rubber 

 begins to stretch, i. e., from 3.5 to 4 cubic meters, depending on the 

 weight it is to carry. The instrument is suspended from a small 

 parachute thrown over the balloon, space being provided for the 

 expansion of the latter to two or three times its diameter or to about 

 twenty times the volume it had at the earth's surface. Sometimes 

 two balloons are used, one of which bursts — the other lets the instru- 

 ment down slowly. Records of temperature and humidity have 

 been obtained at altitudes of 25,000 meters, over 15 miles above sea 

 level with sounding balloons. 



At present about twenty-five observatories — two in this conti- 

 nent, one in India, the others in Europe — are cooperating with the 



