1220 
computers, and (5) introduction of new concepts in 
communication theory. Some of these techniques have 
already markedly influenced the design of meteorologi- 
cal equipment and increased our understanding of the 
atmosphere. An even greater use of this fund of knowl- 
edge will, of course, be made in the future. In the fol- 
lowing paragraphs, a few experimental problems that 
lie within the scope of this survey will be discussed and 
possible approaches for their solution suggested. 
poster 
weer 
{ER 151953 
FEBRUARY 16,1949 
METEOROLOGICAL INSTRUMENTS 
grometer and have placed it in the forefront as a low- 
temperature humidity indicator. Dobson, for example, 
has successfully used this instrument for measurements 
of water vapor from high-altitude airplanes, and re- 
cently Barrett and Herndon [4] have flown the hygrom- 
eter to 100,000 ft using the newly developed plastic 
balloons. Although the equipment used by Barrett 
weighed approximately 46 lb, there is no reason why 
this weight could not be materially decreased by the 
Fie. 9.—An example of a recording showing two distinct cloud decks. (Courtesy, Signal Corps Engineering Laboratories.) 
One of the most exasperating if not the most im- 
portant experimental problem in need of a fresh ap- 
proach is that of low-temperature hygrometry—the 
measurement of water vapor to temperatures as low 
as —80C, accurately, rapidly, and economically. As 
is well known, such standard devices as the hair, gold- 
beater’s skin, electrolytic strip, and wet-bulb ther- 
mometer are inherently poor indicators of humidity 
at these low temperatures. There are, however, two 
quite promising techniques that should be more fully 
exploited, namely the dew-point hygrometer and the 
infrared spectral hygrometer. Such investigators as 
Dobson [11], Thornthwaite and Owen [80], and the 
University of Chicago group [81], have contributed 
significantly to the development of the dew-point hy- 
use of printed circuits, light-weight cuprous chloride- 
magnesium batteries, and a refrigerant such as Freon 
13, and thus make possible flights to 140,000 ft, using 
rubber balloons. The Freon may also be used as a 
hypsometer. With properly employed surface-tempera- 
ture measuring techniques, frost-poit temperatures 
to —80C can readily be measured with a probable 
error of about +0.5C. In addition to research require- 
ments, the dew-point hygrometer should find wide- 
spread use for aerographs and for arctic station observa- 
tions. 
Although a spectral hygrometer using the 6.5-p water- 
vapor band would appear to be an ideal instrument for 
humidity measurements, it has not to date been suffi- 
ciently practical for field use, due in part to the lack of 
