1909.] BY MEANS OF KITES AND BALLOONS. 15 



wind, is in a calm except for its own upward motion through the air. 

 It is therefore exposed in a vertical tube at the top of which is a 

 funnel to insure the passage of a sufficient air current through the 

 tube and about the element. The latter are held by the kites in the 

 horizontal current in which the kite flies. The velocity of this cur- 

 rent is always sufficient to keep the temperature element well venti- 

 lated so that care need be taken only to see that the element is in 

 this current and screened from either the direct or reflected rays 

 of the sun. 



The meteorographs in use need comparison with standard instru- 

 ments, at first to determine their scale values, frequently thereafter 

 to guard against error due to slightly defective elements. Before 

 and after an ascent the instrument is placed in a standard shelter 

 with standardized instruments and allowed to record. Frequent 

 readings of the latter are taken not only at these times but during 

 the entire ascension. A base line for computation of altitudes is 

 thus furnished, also a record of surface conditions for comparison 

 with those of the upper air. To facilitate this computation and 

 comparison, as well as to avoid errors due to the sluggishness of the 

 elements, stops in the ascent and descent are made at frequent inter- 

 vals. These stops need be for but a few minutes. Their times are 

 recorded at the lower station and they are easily distinguishable on 

 the traces. Of course it is impossible to make such stops with 

 sounding balloons, and consequently instruments sent up by means 

 of them should be, to some extent, at least, tested for sluggishness 

 in addition to the tests made for scale values. 



The cellular kite invented by Hargrave or some of its numerous 

 modifications is the one most generally used for meteorological pur- 

 poses. The Marvin-Hargrave kite, in which three planes are put in 

 the front cell and the entire framework strengthened by fine steel 

 wire braces, is the one in use at Mt. Weather. With slight modifi- 

 cations in the size and shape of the planes and in the proportion and 

 distribution of lifting and steering surfaces, this kite has been made 

 to serve in all winds from 3.5 to 22.5 meters per second. The dimen- 

 sions of a medium-sized kite, one well adapted to carrying an instru- 

 ment in winds of from 5 to 10 meters per second, are as follows: 



PROC, AMER. PHIL. SOC. , XLVIII. I9I B, PRINTED JUNE 30, I909. 



