EXPLORING THE UPPER AIR 



us information concerning the direction and the 

 force of the wind at each level which is penetrated 

 by the balloon while it remains in sight. The other 

 type, the sounding or registering balloon, carries 

 with it self-registering instruments and these must 

 be recovered or the records are lost with the bal- 

 loons. Within thickly populated countries, such as 

 most parts of Europe, there is a large likelihood 

 that the balloon will be seen by someone when it 

 descends to the earth, or it may be later recovered, 

 perhaps sometime after it has reached the ground. 

 Attached to the light box of aluminum which pro- 

 tects the instrument is a placard generally written 

 in several languages, and on this it is stated that a 

 small reward will be paid to anyone who will for- 

 ward the box to the address given. It is clear 

 that such a type of balloon is not adapted for use 

 in Greenland where the only inhabitants are in 

 small Eskimo settlements along the coast. It 

 seemed possible, however, that during quiet air 

 conditions we might make use of a new deflating 

 device for the balloon which would cause it to de- 

 scend from any level fixed upon in advance. 



The pilot balloons when inflated with hydrogen 

 in the usual manner are about thirty inches in 

 diameter; the hydrogen with which they are filled 

 is obtained by dropping small pieces of the solid 



49 



