roswell

tuel~ usually give a coating Which is too coarse
grained and heavy. In smoking the drum a long
rod is used as a rotating axis. The drum is ro-
tated rapidly in the flame so as to prevent
overheating and oxidizing of the foil. The car-
bon should not be so thick as to obscure the
metallic appearance of the aluminum foil.
(e) Calibrate the barograph for pressur~. The in-
strument is placed in a bell jar and the air
evacuated. The pressure is kept constant at a
number of pressures so that as the drum turns a
step, record is made on the -.>ked foil. Pressure
recording starts at about 500 millibars so the
first level in the calibration should be at that
value. At each level the pressure should be kept
constant for three to five minutes in order to
obtain a measurable line. Great care and consid-
erable practise are required to control the valves
of the vacuum system so that the pressure does
not change noticeably during each step.
-~~,
The pressure ~teps at which the barograph 18 cali-
brated may be either at regular pressure intervals
. or at the pressure values corresponding to regular
height intervals according to the standard at-
mosphere figures. The recommended steps are
listed below. If the balloon is not expected to
go to the higher altitudes, the calibration may
be stopped at correspondingly higher pressures.
Pressures Standard Atmos~here Heights
500 mb 466 mb corresponding to 20,000 ft.
400 mb 300 mb If II ~o.ooo ft.
300 mb 188.5 mb " II 40,000 ft.
200 mb 117 mb II
" 50,000 ft.
150mb 72.8 mb II II 60,000 ft.
100mb 45.3 mb " II 70,000 ft.
50mb 28.2 mb " " 80,000 ft.
10 mb 17.5 mb " II 90,000 ft.
10.9 mb II II 100,000 ft.
The temperature calibration may be made by recording
two widely spaced temperatures, s.uch as room tem-
perature and the temperature of dry ice (-78°C).
This celibration will be approximately a straight
line and, therefore, two points are sufficient
to plot the curve.
-68-