THE BAROMETER
Whatever the foregoing chapters may imply as to the whole world going
camping the fact is that the woods are still, unfortunately, for the few.
The woodsman must yield gracefully to the suburbanite,--in numbers.
But the weather is for everybody. To be sure the sunrise that talks so
confidentially to the hunter of the coming day does not exist for the
commuter. But the coming day does, even though the things it means are
essentially different. To the hunter with his seasoned clothes and
well-earned health a rain is only of concern in so much as it affects the
business of the day; personally it is of small moment. But to the commuter
what does the weather mean? Dollars and cents, of course. His business
goes on, but to his person one unexpected shower = the cost of pressing a
suit; one thorough soaking = one doctor's bill. For you cannot expect
the man to throw off a chill who can quiet his conscience on the matter of
daily exercise by watering the geraniums and reading the newspaper.
Weather wisdom is necessary for the hunter; for the commuter it pays.
The hunter had to rely on local weather signs. The commuter can go him one
better by investing $10 (how finance will creep in!) in a little aneroid
barometer. The local weather signs were good for twelve hours at the
longest. The barometer is a faithful instrument that adds another twelve
hours to a man's knowledge. Half a day, or even a day before any local
sign of changing wind or growing cloud appears the barometer is on the
job. It will register in Philadelphia the news of a disturbance
approaching the Mississippi. So sensitive is it that it is the slave to
every wave of the great air ocean.
The barometer gauges for the eye the amount of atmosphere that is piled
above one. If the amount is normal and at sea-level the instrument will
measure 30.00 inches. This air pressure is equivalent to a column of water
30 feet high. As this would make unwieldy prognosticators the scientists
use mercury instead, which requires a column less than three feet long.
And for general purposes this is supplanted by the handy little aneroid
(which means "without fluid"). This is so fixed that the pressure of the
air influences the upper surface of a vacuum chamber, balanced perfectly
between this pressure and a main spring. This action is transmitted to an
index hand moving across the dial marked into fractions of inches after
the manner of the recognized standard, the mercurial barometer.
When the warm moist light air of a cyclone invades a locality the pressure
is partially removed, the vacuum chamber is not pressed so hard and the
dial hand or the mercury subsides. When the cold, dry, heavy air of the
anticyclone lumbers in more pressure is applied and the mercury, or the
dial hand, climbs. So a falling barometer means a storm, a rising one fair
weather.
That is a generality that glitters. If that were all there was to it
weather officials would have a sinecure. But each cyclone varies in size,
intensity, and rate of progress. Some do not advance for days. Therefore
there has grown up a pretty large body of information as each storm has
had to be watched and the barometric movements recorded. The most
important variations follow:
Remembering that 30.00 inches is sea-level normal, if the barometer is
steady at 30.10 or 30.20 the weather will remain fair as long as the
steadiness continues, and on the turn, if the fall proceeds slowly with
the wind from a westerly direction fair to partly cloudy weather with
slowly rising temperature will follow for two days.
If the barometer rises rapidly from 30.10 the fall will be equally rapid
and rain or snow may be expected within a couple of days. Since the
depressions of the atmosphere tend to a certain regularity about the
center of the storm it follows that the reactions will follow the actions
in similar manner,--a long rise portending a long fall and a variable
glass meaning unsettled conditions.
The barometer does not rise with wind from an easterly direction unless a
shift is imminent. In winter the air is so much colder over the land than
over the sea that the air brought in by an easterly wind is soon
condensed. Consequently with winds from the south or southeast, even if
the barometer is 30.20 or 30.10 and falling slowly rain usually arrives
(and rain of course is meant to include snow whenever the mercury is below
the freezing point) within 24 hours. If the fall is rapid there may be
precipitation within 12 hours, and the wind will rapidly increase and the
temperature rise.
If the wind is from the east or northeast and the barometer 30.10 or above
and falling slowly it means rain within 24 hours in winter. In summer if
the wind is light rain may not fall for a day or so. If the fall is rapid
in winter rain with increasing winds will often set in when the barometer
begins its fall and the wind gets to a point a little east of north.
If the barometer is 30.00 or below and falling slowly with northeast to
southeast winds the storm will continue 24 to 48 hours. If the barometer
falls rapidly the wind will be high with rain and the change to rising
barometer with clearing and colder will probably come within 20 to 30
hours.
If the barometer is below 30.00 but rising slowly the clear weather will
last several days.
If the barometer is 29.80 or below and falling rapidly with winds south of
east a severe storm is at hand to be followed within 24 hours by clearing
and colder. Under the same conditions but with northeast winds there will
occur heavy snow followed by a cold wave.
If these promises do not always bear fruit it is because they will have
been interrupted by an unseen shifting of the atmospheric weights. But
the barometer will record them. A rapid rise may be checked in ascent and
the instrument may fluctuate like a stock-ticker. Its tale is of very
unsettled weather conditions and consequently no particular brand of
weather will last for very long at a time.
A sudden rise of the barometer may bring its gale of wind as well as a
sudden fall. But the tendency will be toward clearing and much colder.
A fall of the barometer on a west wind is not common. It means rain. A
rise on a south wind means fair. A low barometer and a cold south wind
mean a change to west with squalls for a while. On the other hand, a high
barometer with warmer weather means a shift of the wind to southerly
quarters and an imminent fall.
If the barometer rises fast and the temperature does, too, look for
another storm. This is often noticed in summer.
There is a slight daily oscillation of the mercury, which, if other things
are steady, registers highest at 10 A. M. and 10 P. M. and lowest at 4 A.
M. and 4 P. M.
If this data confuses bear in mind the simple ordinary progress of the
barometer in the usual storm: First, it will stand steady for a day or so
at any point between 30.10 and 30.50. Then the glass will begin (for most
storms) to fall gradually. As the center nears the fall hastens. After the
lowest point has been reached a slight rise will be followed by another
slight fall and then the final long rise will commence. The rain begins
and ceases at different stages for different storms, depending upon the
wind's velocity and direction.
For every 900 feet of altitude the height of the mercury is about one inch
less. Do not complain that your barometer is inaccurate if you are living
up in the mountains and your readings are not the same as the weather
reports which are reduced to sea level. All the figures given in this
chapter are for sea level and if your house is 1900 feet above you must
move the copper hand of your aneroid 1.95 inches from the pressure hand.
If the pressure hand would read 28.05 the adjustable copper hand would
read 30.00 which is the sea level reading.
One good thing to remember is that a barometer falls lower for high winds
than for heavy rain. A fall of two- or three-tenths of an inch in four
hours brings a gale. In the ordinary gale the wind blows hardest when the
barometer begins its rise from a very low point.
In summer a suddenly falling barometer foretells a thunderstorm, and if
the corresponding rise does not at once take place the unsettled
conditions will continue with probably another thunderstorm. If you see
the thunderstorm first, that is, if the barometer is not affected by the
approaching black cloud you may be sure that the storm will amount to
nothing.
The man in the fields or along the shore has many natural barometers in
animal life. But these natural barometers only corroborate; they do not
foretell, at least very long before. Some are useful at times and among
these the birds are foremost. The observant Zunis have incorporated this
in one of their pretty proverbs, "When chimney swallows circle and call
they speak of rain." As a matter of fact the swallows are circling most of
the time after insects. If they are flying high it is because the bugs are
flying high and that is because there is no danger of rain. As the rain
nears the air gets moister, the bugs and the birds fly lower.
Whether they do this because their instinct is to avoid a wetting or
because the lighter atmosphere of a cyclone makes flying more difficult,
particularly at altitudes, I do not know. For weather purposes it is
enough to watch their comparative levels. Wild geese are excellent signs,
I am told, but it would be a dry country that waits for a sight of them
for its rain.
Bees localize before a storm and will not swarm. Flies crowd upon the
screens of houses when humidity is high, possibly because the appetizing
odors from within are buoyed afar by the heavy air. Cuckoos seek the
higher ground in fair weather and disappear into bottom lands before a
rain. Although they are called rain-crows they are heard in all weathers.
Smoke is as good an evidence of barometric pressure as anything except the
instrument itself. On clear, still days it will mount; on humid days
without wind it will cling to the hill. There is that difference. But it
takes skill and many comparisons to gauge its angles in the wind. It
becomes a test in observation and finally rewards one by becoming an
excellent sign not only of air texture but of the direction of its
currents.
No reference to barometers would be complete without mentioning spiders.
They show a most delicate apprehension of changing conditions. If the day
is to be fine and without wind they will run out long threads and be
rather active. If the rain is nearing they strengthen their webs, shorten
the filaments and sit dully in the center. Fresh webs on the lawn insure
a clear day. But for the commuter, whose time is money, there is little
leisure to consider the spider.
As a natural result of the variation in altitude affecting the barometer
the words which are printed on the face become entirely useless. In some
places it would be impossible for the needle to point higher than "Very
Stormy." Even at sea level a sudden fall to "Fair" would cause a rain,
much to the indignation of the person who thought that he had purchased a
self-registering weather prophet. Disregard the words but watch the needle
and you will never be surprised at what the weather is doing next.