Evening star., 1938-03-24
STARS, MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study.
RY TuOMhc uEHDv
BY THOMAS R, HENRY.

Another Job has been found for the
Bureau of Standards sky exploring robot
balloonist-that of measuring the thick
ness of clouds.
In other words, another sensory area
has been added to the delicate little
mechanical brain of the lifeless aeronaut
who can soar beyond the utmost human
limits with no errors of Judgment, no
danger of fainting from lack of oxygen.
no suffering from the intense cold OF
outer space.
Already it has made accurate reports
on temperature, humidity, wind direc-
ton, ultraviolet light intensity, cosmic
rays and the electrical properties of the
air. In the measurement of cloud
heights and thickness a photoelectric
cell is used which varies its electrical
resistance inversely as the amount of
light falling upon its window. This con-
trolls radio signals sent to the ground.
When clouds are present the amount
of sunlight penetrating the window is
reduced. Hence, when the balloon is
below the clouds the photo cell resistance
will be high and the audio note measured
by the recorder on the ground quite low.
AS the balloon penetrates into the cloud
the photo cell is exposed to more and
more light. Finally upon emerging from
the top of the cloud 1t is exposed to full
sunlight.
Thus the thickness of the cloud is sig
nailed to the ground. Measurement of
the barometric pressure shows at what
attitudes the balloon penetrated into
and emerged from the cloud. The new
development is the work of Harry Dia-
mond. w. S. Hinman. jr.. and F. w. Dun
more of the bureau staff and is described
in the latest issue of the Bureau of
Standards Journal of Research.
The little robot weighs only about two
pounds. Its exploring trips into the
stratosphere are by no means necessarily
fatal, since it often parachutes to safety.
Another new instrument is an absolute
electrometer perfected at the Bureau by
Herbert B. Brooks, Francis M. Defan-
dorf and Francis B. Silsbee. The instru-
ment goes back to the principle of an
electrical measuring device more than
century old and long since abandoned
by engineers.
In the days of Benjamin Franklin
almost the only known manifestations of
electrical forces were those associated
with the storage of very tiny quantity of
electricity at rather high voltage. For
the most precise Guantitative measure
ments of such voltageS Sir William Snow
Harris devised 100 years ago an elec-
trometer in which the attraction between
two oppositely charged metal disks was
weighed by chemists balance But
almost simultaneously with his inven-
ton the researches of Michael Faraday
on the manifestations of electricity when
circulated in much larger quantity at a
very much lower voltage by dynamos
swung the trend Of thought in a new
direction and led to the development of
the present electric power industry.
Successive improvements in technique
and the constant economic pressure for
transmitting larger amounts of power
over greater distances at higher efficiency
have led year by year to steady increase
In the voltages used. The precise meas
urement of these high potentials In
terms Of the small unit, the volt, agreed
upon in the infancy of electricity, has
become increasingly difficult as the guam
t1ty to be measured has become hundreds
of thousands of times the international
standard.
AS result, the bureau announces, the
pendulum now has swung back and the
three engineers have perfected an in
strument based on the principle of
Harris two disks, but 100 times more ac-
curate and calculated to measure voltages
ten times as great. The electric attrac.
ton exerted On Q Hight aluminium disk,