Evening star. [volume] (Washington, D.C.) 1854-1972, 1889-01-17
PREDICTING THE WEATHER.
Reducing the Barometric Readings to
the Sea Level.

The signal Office man was resting from his
labor OF making the morning map and was
looking YEARLY at the colored pencil marks
before him when STAR reporter entered the
room this morning and informed the prophet
that he had come to talk about the weather.
Probabilities smothered a sigh with a smile, as
though the subject were bit wearisome to
him and yet he considered it a part of
his duties to submit He explained that
the present bad weather is the re
suit OF large storm prevailing
near the great lakes. drawing great quantities
of warm, moist air over the land from the ocean
and producing the misty rain that has pre-
vailed. This storm, he said, entered the coun-
try at the extreme northwest corner and has
moved almost in a semi-circle. first going south
where in New Mexico and making line for the
lakes.
while the storm was passing along the
western coast" he added, 1--WE probably made
some errors in drawing the lines of barometric
pressure, because we have as yet only an i'm
perfect formula for reducing the readings to
the sea-level"
what is that?" asked the reporter.
II say that our reductions to sea-level are
not as perfect as they might be, and we con-
| sequently often get our barometric readings
too low You see there is less pressure on the
mercury of the barometer as we ascend. owing
to the air growing lighter and the readings
made in high places indicate with accuracy the
atmospheric conditions in the surrounding
country"
A MATHEMATICAL FORMULA.
- So, in order to secure general correctness we
have to devise q mathematical formula by
which these readings, taken at an elevation,
may be reduced" to the corresponding rela-
tive re adings that would have resulted had
they tax or no xvh IL
point of greatest atmospheric pressure. Now
in the extreme western part of the United
States the mountainous character Of the coun-
try makes it necessary in a great many in
stances to locate very important stations on ex-
Temely high places, and the result is that with
the reduction formula we now have the read.
ings from these stations, do not represent the
exact state of things. The construction of q
formula is a difficult problem, and one re-
quiring years of experimenting.
LOCATING STATIONS.
'We often have letters here" he continued
''from all over the country stating that they
have elegant locations for signal stations which
they think we will greedily lease; these are
almost invariably situated on hill tops or noun
are strongly urged upon u.s. We have to ans
wer such letters by telling the writers that we
don't want to perch our stations of hill tops
but that we are aiming to get them down as low
a we can. To be sure, there may be some
very interesting experiments made from high
places, experiments that may, in the end, be OF
value; but the disadvantages of such places are
many and great. 1t may be possible, if we had
| a very high station to get warning Of an on
coming storm by means of the appearance OF
the cloud-bank on the horizon. but at best the
advantage gained over an observer down at the
| sea-level would be that of few minutes.
"At the same time think that some very
interesting experiments could be made with a
thermometer and barometer on top of the
Washington monument. We might be able to
learn something about the movement and con-
dition of the air above us during the preva-
lence of storm, and it might lead us to dis
cover more correctly the nature of storms in
general Yet would not consider it advisable
to locate our observing station there. Inas-
| much as we live on the surface it is expedient
to make our observations on our own basis,
and all that we may learn beyond them is only
interesting material"