The San Juan County index. (Aztec, N.M.) 1890-19??, 1899-09-01
TELL THE WEATHER.
HOW TO LEARN HOW HOT AND
HUMID WE ARE.
n sharpa. Too. Are Able 70 Guess on
tho Prospects Of Cool Waves aud
Their Duration-Pesp ne the United
States Bureau.

An sorts Of instruments and appa-
ratus are used by the United States
Weather Bureau to determine meteor
illogical conditions and prospects. For
measuring the exact temperature at It's
various stations are the thermograph
and the maximum and minimum Their
mometers. The former gives a CON
tinuous record Of the temperature; the
latter two show respectively the high
est and lowest for each twenty-four
hours. For studying the pressure Of
the atmosphere, the stations of the
weather bureau are equipped with self
registering aneroid, paragraphs and
mercurial barometers. Readings from
both r corrected for the attitudes OF
the station, and the latter for varia-
lions in temperature. The determine
ton Of humidity, or relative humidity.
as it is called by the weather bureau,
is accomplished by means Of two Their
mometers, the so-called dry-bulb and
the wet bulb. The first is the ordi-
nary thermometer, by which the tenn
perature is indicated. The second IS
similar. except that the mercury bulb
is surrounded by a cloth, which may
be saturated with water. When this IS
done, air is made artihcially to pass
over the saturated cloth, which causes
the water to evaporate rapidly. The
heat which is rendered latent by this
process comes from the mercury of the
thermometer, making 1t descend in the
tube with a rapidity proportional to
that Of evaporation. In dry air the lat
ter process is much more rapid than
in damp air, and by noting the differ
ence of the reading Of the dry-bulb
and wet-bulb Instruments, and making
a simple mathematical computation,
the relative humidity is determined. It
is read in hundredths, 100 meaning air
saturated with moisture, and zero, air
free from 1t. The former point is some
times reached, though never the latter.
The signal service makes use of two
instruments in studying the wind-a
vane with automatic electrical indica-
tor for showing it's direction and the
thermometer for registering the veloc-
ity. Both of these are exposed to the
unobstructed violence of the wind,
though connected electrically with the
indicators which are In the Office be-
low. Both the instruments register
continually upon a drum revolved by
clockwork, and at any time the direc-
ton and velocity of the wind can be
seen at a glance. The apparatus used
by the weather bureau for determining
the character of the day is known as
the sunshine recorder" It consists
Of a thermometer, with its bulb black
ened to increase the absorption of heat
from direct sunlight, inclosed In a
vacuum tube, to prevent as far as pos
sible the direct influence Of the tenn
p%erature of the surrounding air. The
piece Of apparatus is In such a posi-
ton as to receive the suns ravs the
entire day. When the direct rays
strike the blackened bulb the mercury
suddenly rises and closes an electrical
circuit, which aus a record to be
made upon the revolving drum in the
office below. When the sun is obscured
the mercury drops again, and the cir
cult Is broken. The computation IN
tenths of the possible sunshine hours
is made by the weather official. The
latest device used by the weather bu-
reau for measuring the precipitation
consists of a hopper or scale pan.
which is constructed so as to tip and
empty itself, and at the same time
make an electrical indication Of the
fact in the office below for each one
hundredth Of an inch precipitation. BY
counting these records upon the re-
volving drum the officers can tell the
exact time the rapidity and the amount
OF precipitation for each shower or pc
riod of rain.