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INSTRUMENTS
METEOROLOGY
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BAROMETERS
Barometers measure atmospheric pressure, that is to say the weight of the air column
above our heads. High pressures (anticyclones) usually mean fine weather while low
pressures (depressions) are associated with bad weather. But this is a little too simple
and barometer readings should be interpreted in respect of sudden or slow pressure
changes. Seasons should slso be taken into account as well as types of wind, humidity and
high altitude phenomena.
Sudden fall of pressure:
This may mean that rain is on the way.
Regular fall of pressure:
If the weather is fine, there should be no change.
Steady rise of pressure:
A slow and regular rise of pressure means that fine weather is on the way.
Sudden rise of pressure:
A sudden rise in barometric pressure after a time of low pressure is an indication that
the fine weather will not last for long.
There are aneroid, mercury and water barometers. The aneroid barometer is made with a
vacuum capsule which becomes compressed according to the atmospheric pressure and
transmits variations to a dial needle. The mercury barometer consists of a glass tube
filled with mercury under the vacuum column, varying with the atmospheric pressure which
is of 760 mm at sea level. Water barometers, which are used mostly for decorative
purposes, consist of glass balls with a long narrow neck in which a coloured water moves
up and down. Recording barometers show variations over a period of 24h or 7 days on
a paper strip that operates with a clock mechanism
Aneroid Barometer
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The aneroid barometer is made with a vacuum capsule which becomes
compressed according to the atmospheric pressure and transmits variations
to a dial needle |
Description and Operation
Disregard the words Stormy, Rain, Change, Fair and Dry as these are only
traditional zones on a barometer dial. Your barometer indicating hand will
never move all the way to Rain to predict rain or to Stormy to predict
inclement weather. The normal operating range of movement for your barometer
indicating hand is from 1000 to 1030 hPa. Your most extreme readings would
occur before a hurricane or tornado when barometers have dropped as low as
970 hPa (28,5 inches of mercury); or, at the other extreme if very fair, dry
weather is to come, your barometer may rise to 1050 hPa (30,9 inches of
mercury). The following procedure, if done every 12 hours, or morning and
evening, should give you the best results.
1. Tap the instrument lightly to release any latent action.
2. Adjust set hand directly over the indicating hand. This is your momentary
reading. At a later period you will be able to notice in what direction the
indicating hand has moved since the last setting.
If it moves to the right you have a rising barometer which usually means a
change for the better or continued good weather. If the reading is to the
left you have a falling barometer, which usually means a change for the worse.
A steady barometer means no change. For accurate weather predictions, it is
highly important that your barometer be adjusted to sea level. The correct
sea level reading can be obtained from your Weather Bureau or television
weather forecasts. Readings obtained from your barometer indicate weather
conditions that may prevail within the next 24 to 48 hours, providing wind
direction and velocity remain the same as when readings were obtained.
Adjustment of the Barometer
In the event that your barometer does not read exactly like the reading
obtained from your local weather forecast, the instrument should be adjusted.
The indicating hand of the barometer may be adjusted by turning the set screw
in a smal opening at the bottom of the instrument. A smal screw driver may be
used to turn this screw.
Toricelli Barometer
| Toricelli mercury barometers measure continuously the
changes in air pressure. To estimate
forecasts, one has to set the index on the glass tube to the actual
mercury level. The tendency of the atmospheric air pressure and the amount
of change make a reliable forecast possible..
Evangilista Toricelli was an Italian
Scientist in the seventeenth century (1608-1647). He was looking for a way
to prove that the air had a certain weight.
He took a glass tube, enclosed at one
side, and filled that tube completely with mercury. Now all air was out of
the tube. He locked the tube on the open side with his thumb and turned
the tube upside down in a reservoir, filled with mercury. Now he released
his thumb and he noticed that a certain amount of mercury was kept in the
tube. The air pressure on the surface of the mercury in the reservoir
pushed the mercury column up and down in the tube.
He noted an average height of 76
centimeters after repeating the experiment. One other observation was,
when the column mercury went down, the weather went bad, and when the
mercury climbed up in the tube, the weather changed to fair. This was the
birth of the first actual and reliable weather instrument.
The Mercury Barometers, Instruments of Precision, measure Atmospheric
Pressures. The superior sensitivity is not to compare to any others
instruments from the mercury column, and they have no moving metallic
pieces, whereby all attention and service escape. The Precision is
constant in time.
Our refinery constructed Barometers of different Models (in heavy Wood or
other Materials) are very decorative and also make fine Gifts. Through
attentive observation, it is possible to watch meteorological Evolutions,
and also they become precious Hobby objects.
INSTRUCTION CONCERNING THE USE OF THE MERCURY BA
ROMETERS ACCORDING TO TORRICELLI
BAROMETER TRANSPORT
Instructions on the use of the "Torricelli" mercury barometer
This sensitive and very reliable barometer is fragile to transport.
We use a patented system of blocking the column of mercury which still
allows some dilation/expansion. Despite this, a bubble of air can appear
in the main column, thus distorting the results. Only if this occurs is it
necessary to take the following remedial action:
-Incline the Barometer to 45 °, angle until
you hear the mercury hitting against the other extremity of the Tube.
- leave the obturating system (blocking device) in place with the stopper
well screwed up.
- turn the barometer upside down and knock it gently against a piece of
wood protected with a shock absorber ( plastic foam, thick tissue, rubber
strip).
The bubble will climb just up to the bend, where it will cause no more
problems.
Bringing the barometer into service
1. Keeping the instrument upright, give several light taps in the area of
the reservoir stopper in order that the mercury drops into place.
2. Incline the barometer about 45 degrees and, supporting the reservoir
with one hand, gently unscrew the stopper and lift it away.
3. Remove the obturating system (blocking device)
4. Put the stopper back in place without screwing it up fully; the give in
it's thread is enough to balance the atmospheric pressure and keep dust
from getting inside.
5. Gently return the barometer to normal position, hang it vertically and
it
is ready to work.
Transporting the barometer
1. Incline the barometer about 45 degrees, just until you hear the sound
of the mercury moving to the top of the tube.
2. Put the obturating system (blocking device) back in place.
3. Supporting the reservoir with one hand, screw up the stopper fully but
not too tight.
Altitude adjustments
A mercury barometer always gives an atmospheric pressure reading which is
true to the place where it has been set up. To use it from a
meteorological point of view, it is necessary to know what the pressure
would be at sea level.
To adjust for this you need to know the altitude of the place where the
barometer is set up.
The town hall, or some tourist guides can provide this information.
The instrument has a movable reference plate with a scale up to about
760mm.
It is enough to position the reference marker of this plate against the
appropriate altitude setting. One then has only to read the corresponding
value on the atmospheric pressure scale of the movable plate.
Example: finding your altitude to be 750m, you place the variable 760
plate scale to correspond to mark 696 and from then on all meteorological
variations can be read solely from the plate.
Important
All our barometers come with a mobile indicator in order to show
atmospheric pressure variations in a relatively short time. Therefore the
weather forecast is effected not from the value of one measurement at a
given moment, but works by sensing variation in atmospheric pressure, the
size of this change and the speed of the change.
Interpretation of results
- slow fall of the barometer of 2 to 3 mm in 24 hours = far off
depression
without any significant change in the weather
- fall of 1 to 2 mm an hour = weather disturbances on the way with short
downpours
- major fall of 6 to 10 mm in 4 to 5 hours = storms, tempests, violent
winds
- slow fall, weakly continuing = persistent bad weather
- rapid rise = fine weather of short duration
- regular rise = dry fine weather or, in winter, dry cold
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Huyghens mercury-contra-barometers measure continuously
the changes in air pressure. To estimate
forecasts, one has to set the index on the glass tube to the actual
mercury level. The tendency of the atmospheric air pressure and the amount
of change make a reliable forecast possible.
Christiaan Huyghens was a Dutch scientist
who lived in the seventeenth century (1608-1647). He is known for several
inventions and discoveries, all in some way related to shipping.
He solved one of the major problems that
the Toricelli weather instrument showed: the degree of readability. He did
this by placing a "multiplication" onto the mercury tube. In the now
U-shaped instrument colored alcohol was filled onto the mercury surface.
All changes in the mercury column where multiplied with a factor ten, and
transferred to the surface of the colored alcohol. The scale of the
Toricelli became tenfold enlarged, and due to the colored fluid, accurate
and even from a distance to read.
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Eco-celli
barometers
| General
The Eco-celli is a new development in ecological barometers. Dingens
Barometers registered and patented their invention on August, 24th 1998.
- Key Benefits
- Contains no mercury
- 4 times enlarged scale
- Easy and safe to transport
- Environmental safe
- Principle
- The with red silicon-based fluid and gas filled
- U-shaped tube is the barometer part of the instrument.
- Air pressure is measured by the red fluid.
- The right-hand precision-thermometer is filled
- with blue colored methyl-alcohol.
- Temperature is measured by the blue fluid.
- The error margin of temperature in the air pressure
- values is corrected by setting the moveable scale
- to the surface of the blue fluid in the thermometer.
- The air pressure can be read by setting the second
- index to the red fluid level.
- The amount and direction of changes in air pressure
- between the previous index setting and the current
- one, result in a reliable forecast.
- Versions
- Indications are in centigrade (temperature) and
- hectoPascal (air pressure).
Measurements
- U-shaped tube: length = 82 centimetres,
- total width = 4 cm, tube diameter = 0.7 centimetre
- Thermometer tube: length = 82 centimetres,
- tube diameter = 0.7 centimetre
- Thermometer scale: 0°C - 50°C
- Barometer scale: 975 hPa-1054 hPa
- (dimensions: 25 cm x 4 cm)
The Eco-celli is a new type of barometer with the same precision as a
mercury-barometers. Yet the basic principle is completely different. In
stead of Mercury, as in traditional fluid-systems, the functioning is
based on the compressibility of gases. On the upper left hand of the
barometer you can see the gas above the red fluid in the reservoir. This
gas provide a constant counter-pressure against the atmospheric air
pressure.
A very important factor in measuring with barometers is the
temperature. Due to high temperatures, fluids and gas will, expand,
causing an error in the readout on the scale. The Eco-celli does not have
that problem. In the construction of the Eco-celli a high precision
thermometer is used, mounted parallel to the barometer. This thermometer
has the same expansion/compression-rate according to the temperature.
With the help of a moveable scale, one sets the scale to the actual
temperature (blue fluid level). The error caused by the temperature is so
automatically corrected and one can read the correct air pressure.
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Water barometer, also known as Stormglass,
Goethe-barometer,...
| This invention of Gheijsbrecht de Donckere, a
Dutch "noble man" was made in the 16th Century. This weatherglass should
give farmers an indication about the coming weather. The German writer and
poet Goethe discovered this barometer on one of his travels and he
introduced the instrument in the German speaking countries. Soon the real
inventors' names was forgotten and the barometer came to be known as
Goethe-barometer.
A glass bottle with a tulle is enclosed
at the top. There is only one opening, via the tulle. Water (preferably
colored) is filled into the bottle, just above the base of the tulle. The
air pressure of that moment is enclosed in the water barometer. One can
see the rising and falling of the colored water in the tulle according the
changes of weather. The changes, the speed and the direction of changes
show the changes of weather to come.
Due to the properties of water and air,
this type of barometer can not measure exact air pressure, but it is
sufficient for a more or less rough forecast.
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Tendency
barometers - Adie
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Tendency barometers show tendencies of air
pressure, rather then actual values. One can, if one chooses, recalculate
these tendency values in order to become the actual values. To estimate
forecasts, one does not need to know the absolute air pressure values, but
it is essential to know the tendency of the atmospheric air pressure and the
amount of change.
Based on the
principle of Alexander Adie, a Scotsman from Edinburgh, a new type of mobile
barometer was introduced in the Winter of 1818. He developed
his "portable barometer" for nautical conditions. This kind of
barometer was frequently used by seafaring nations in the period between
1820-1870.
With the
introduction of the mechanical barometer around 1870, this type of barometer
was replaced by the aneroid barometer, which was better suited for rough sea
conditions and only a little bit less accurate.
This instrument consist of 2 elements: one tube in U-form, filled with
red liquid and one thermometer (blue liquid), mounted in parallel, next to
each other
- Both liquid levels equal: change
- Red liquid level below the blue liquid level (high pressure): fair
- Red liquid level above blue liquid level (low pressure): wind - rain
Tendency dial Mark the differences between the liquid levels on the
upright dial. The changes in tendency allow it to predict correctly the
weather changes in Your very own micro-climate. |
Digital barometers
| Digital barometers measure air pressure less accurate then
fluid barometers. This is due to their construction. A little suppressible
element is changing the electrical impedance. A built-in chip calculate
out of the measured value and stored air pressure values the actual
air-pressure. This air pressure is shown on a display. The accuracy of
measuring is dependant on the accuracy of the suppressible element.
Digital barometers are mostly equipped with tendency, memory, temperature
and humidity modules. Deviation of the measured values can be up to 15 %.
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Barometers must be adjusted with regard to altitude and mean pressure. As you go up,
the pressure goes down but not in a linear way. Atmospheric pressure can be measured in
mercury millimeters (mm hg), in millibars (mb) or hectoPascal (hPa), the last two units
being equivalent
Absolute Atmospheric pressure and relative
Atmospheric pressure:
p
abs
= Absolute Atmospheric pressure [hPa]
p
red
= relative Atmospheric pressure at sea level [hPa]
p= Pressure differences [hPa]
h= Altitude above sea level [m]
 Encylopedia Wikipedia, The barometer
Orders Through
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