322 THE EXPLORATION OF THE FREE AIR. 



this knowledge has been gained by meteorological stations on moun- 

 tains in various parts of the world, yet these observations, which have 

 the distinction of being the only long-continued ones possible at a fixed 

 height, are affected to a greater or less extent by the mountain itself, 

 and so do not give the true conditions of the free air. Balloons carry- 

 ing aeronauts have long been used for this purpose, but the results 

 obtained, from a meteorological standpoint, are incommensurate with 

 the expense and risk incurred. Nevertheless, at the last international 

 meteorological conference in Paris it was voted to recommend the use 

 of balloons, both captive and free, which carried aeronauts, and free bal- 

 loons provided only with automatic instruments to record at far greater 

 heights than man can live. The successful experiments with kites at 

 Blue Hill led to the recommendation that this method also should be 

 included in the international scheme for exploring the atmosphere. 

 An international committee, of which the writer is the American mem- 

 ber, was appointed to carry out the recommendations. International 

 cooperation in the work with balloons has been secured in Europe, but 

 in America attention has been given chiefly to kites. To obtain the 

 atmospheric conditions up to a height of at least 10,000 feet, kites i)re- 

 sent many advantages over free balloons whenever there is wind. Cap- 

 tive balloons, besides being more expensive than kites, can not attain 

 nearly so great heights on account of the weight of the cable necessary 

 to control the balloon. Kites then have these points of superiority: 



1. Econoray in installation and working. 



2. Accurate determination of height by angular measurements. 



3. Adequate exposure and ventilation of the thermometers which in 

 a balloon are bathed in heated and stagnant air. Therefore the tem- 

 peratures observed at a given height in a balloon are generally warmer 

 during the ascent than during the descent, which is not the case with 

 kites. 



4. The possibility of making frequent ascents and descents permits 

 observations to be obtained almost simultaneously in different air strata 

 and nearly over a station at the ground where there may be instruments 

 recording simultaneously. 



On the few occasions when the wind is lacking near the ground there 

 can be substituted the "kite balloon" already tried in Germany, which 

 will always carry instruments to moderate heights, because it is not 

 driven down, like the ordinary captive balloon, by the high winds 

 which prevail in the upper air. 



The advantages of kites are now becoming recognized, not only in 

 this country, but abroad. Our Government Weather Bureau has 

 expressed its intention to equip 20 stations with kite appliances to 

 obtain synoptic data at the height of a mile in the free air for fore- 

 casting. In Europe the Blue Hill expeTiments have been repeated at 

 Paris and at Strassburg. 



About 200 records from kites have been obtained in the free air at 



