Evening star. [volume] (Washington, D.C.) 1854-1972, 1894-07-30
BREATHING SPELL
The Thunder Storm Yesterday Made il
Cooler Today.
How the Temperature is Recorded nj
the Weather Bureau-PhOtO-
graphing Lightning.

There were thunder storms all over the
Middle Atlantic states yesterday afternoon.
Washington had very welcome one, dur
ing which a third of an inch of rain fell,
and the thermometer was knocked down
from % to 40 degrees in very short while.
Consequently, when night came on the air
was balmy and cool. and it didn't take any
rocking to put Washingtonians to sleep
when they retired for the night The mer-
curry remained around II and ~ degrees un-
til q O'Clock TINS morning, and then it ap-
peared to recover from the jealous slap that
Jupiter PiuviUs had so severely dealt it a
dozen hours or SO before, and began to
climb upward with much vigor.
At l o'clock today the instrument at the
weather bureau indicated 81 degrees, and
Prof Williams said he believed that the
maximum today would hot be more than
.6. The baromeSrical conditions over
the country this morning We're the same as
those that preclpitated the intensely hot
visitation of Friday, Saturday and yester-
day. There is a low barometer way up in
the northwest, with high lowering around
the Middle Atlantic coast, so we can expect
to have it a good deal hotter during the
next day or SO. The lightning played right
vividly last night after the gust in the
afternoon had gone by, but it was too far
away to be photographed with much sue
cess. Every time there is local thunder
storm at night, however, pictures are taken
at the fiery electric flashes.
How Ii is Done.
One of the most interesting features in
connection with the weather bureau is the
method of recording the official tempera-
ture. 1t is notable fact that the official
record is always considerably lower than
that secured by private instruments scat
tered around in more exposed parts of the
city. AS result of this fact, light and
airy newspaper paragraphers are wont to
say that the official thermometer is kept
in an ice chest. In reality this is not SO.
The recording Instruments are kept i'll an
apartment made for the purpose above, a
sort of cupola on the roof of the weather
bureau, and perhaps fifty feet above the
level of the street. 1t Is in an arrange
ment slightly suggestive of a dove-cote. 1t
has double roof. with free circulation
OF air. in order that the temperature in
side may not be above the normal. The
sides are of lattice work, allowing a free
Circula ticn of air, but at the same time
keeping out the direct rays of the sun and
the influence of radiation from asphalt
streets or light-colored walks.
The object in secluding the thermometer
in this way is to secure the exact tempera-
ture of the air itself, and this it does,
though, of course, ii does not give the
record of heat which pedestrians are COM
PEELED to withstand as they walk along the
sunny side Of The avenue. The tempera-
ture which we actually feel is dependent
upon so many circumstances that it would
be impossible to make any record of it
that would be worth while or that would
be OF use FOR purposes oc comparison. Ac-
3crdins 80 Prof Garr!ott. he forecast off,
Ger at the weather tureau, the change of
temperature for elevation is only one de-
gree for every 500 feet, so that the change
effected by keeping the official instrument
above The roof is a very small fraction of a
degree. In other words, the temperature
there Is Just about what it would be a few
feet above a grassy lawn, for example,
where the influence of reflection and radia-
ton would not be felt. The two instru-
ments OF which especial reliance is placed
have, of course. been tested and proved to
be as accurate as instruments of that sort
can be- The, are mounted on the ends of
two rods. so that by turning a crank they
can be mad" to revolve with great rapidity
through the air This is always done before
an observation is taken, so as to stir up
the air inside the little house and prevent
the thermometer from being unduly af-
fected by any layer Of dead, warm air
which may have settled there