Introduction: Barometric Mason Jar

Weather an everyday preoccupation over which we have no control but affects our daily lives in so many ways.

How do we know what the weather will be like from day to day, check the weather bulletins, look out of the window or monitor it yourself.

Using a STEAM approach you can create basic tools to aid in weather forecasting.

Science - Any system of knowledge that is concerned with the physical world and its phenomena and that entails unbiased observations and systematic experimentation.

Technology - Methods, systems, and devices which are the result of scientific knowledge being used for practical purposes.

Engineering - Scientific principles to design and build machines, structures, and other items.

Arts - The expression or application of human creative skill and imagination,

Mathematics - The abstract science of number, quantity, and space,

We will be observing the effects of the weather by using a device that responds to atmospheric pressure and by gathering and analysing the data gain an insight into the relationship between the two.

One simple method to monitoring atmospheric pressure is a Barometer were we can get an indication of the likely weather conditions.

Barometer, a device for measuring atmospheric pressure and predicts changes in the weather.

Atmospheric pressure equates to 1.03 kilogram force per square centimetre, though in reality its affected by weather conditions, altitude and temperature.

There are may types of Barometers but the simplest and earliest forms are water based.

This Instructable will focus on a water based Barometer, although the aneroid variant could also be made.

Our simple water based Barometer is not an absolute indicator of weather being a gauge but can complement other data such as wind direction and temperature to provide a more informed assessment.


Mason Jar

Clear or translucent plastic tube or Straw


Food Colouring or Dye (Optional)

Grommet and/or Silicone sealer.

Drill bit (slightly larger then the straw to enable the grommet to be fitted and create a snug fit when the straw is inserted.).

Short ruler.

PTFE tape

Step 1: Methodology

How does the Barometer work.

It works on the principle of pressure differential.

The difference between the air pressure in the upper part of the jar compared to the atmospheric pressure pushing down on the exposed end of the straw. Hence the reason for leaving the end of the straw open.

As the atmospheric pressure increases a force is exerted on the end of the straw which pushes the water this then applies pressure inside the jar trying to compress the air in the upper part of the jar.

As the atmospheric pressure decreases the force exerted on the end of the straw reduces, the opposing force from inside the upper part of the jar pushes against the water and the level rises.

These changes in atmospheric pressure coincide with the weather conditions, higher pressure for more favourable weather and lower pressure for more inclement weather.

Therefore by monitoring the level of the water in the straw we can get a determination of the atmospheric pressure and from this the weather.

Step 2: Preparation

Take the Mason Jar and remove the lid, setting the jar aside for the time being.

Some Mason jars come pre prepared with hole in the centre of the lid and a straw and this will make the preparation a little easier.

If this is not the case then a hole will have to be drilled in the centre of the lid.

The hole in the lid should be slightly larger than the straw to accommodate a grommet and once the straw is fitted in the grommet it should form a air tight seal when the lid is screwed onto the jar.

The straw should be a tight fit and not too easy to slide into the grommet, if it slides in too easily air will escape and the Barometer will not work.

If the straw is too loose in the grommet get a smaller bore grommet, or a wider straw.

Additionally, silicone seal can be applied around the grommet and straw to seal any gaps but only after the height of the straw has been adjusted so that its bottom is one 1/4 of the height of the jar from the bottom.

A thin line of Silicone seal may also be required around the rim of the jar to aid sealing or PTFE tape can be wrapped around the the rim too.

If using Silicone seal ensure it is fully cured before further assembly.

Step 3: Testing

Once the assembly is complete the jar should be tested to ensure there are no leaks around the seals for either water or air.

Simple tests.

1:Dry test.

With the lid and straw assembly firmly in place, suck on the straw after some initial removal of air there should be resistance to any further air removal unless there are any gaps.

Any gaps should be sealed with further PTFE tape, silicone sealer or a gasket.

2: Wet test.

Fill the jar half full with water tip the jar lid side down and check for any leaks, repair if required repeat the same process as in test 1 again fixing any leaks.

All these tests should be successful before continuing.

Step 4: Setup

Half fill the jar with water.

At this stage if required colour can be added to the water to aid visibility.

Attach the lid firmly.

If there is no water in the part of the straw extending above the lid add some water slowly via the tube opening until the wafer level is at least 2/3rd of the way up the exposed part.

In the event that the water does not stay within the upper part of the tube a leak exists which needs to be sealed.

If the wafer stays in the upper part of the tube after several hours mark the level.

Tape a short ruler to the tube to enable the height of the level in the tube to be recorded.

Alternatively mark graduations on the tube that mirror the graduations on the ruler.

Set the jar aside in an area not subject to extreme temperature fluctuations, not near a radiator or on a window sill.

The heat will cause the water and air in the jar to expand and the level will rise and be misread as low atmospheric pressure.

Also over time water evaporation will occur reducing the level which will require replenishing.

However, do not seal the end in the tube in a bid to prevent water evaporation as this will prevent the Barometer functioning.

The water level at the time of setup is relative to your locality and the weather conditions at this time.

Try to pick a day where the weather is not at extremes but in between.

If this is not possible it's not a major issue it just means that if it was setup during a high pressure period the level will extend above this point for low air pressure, with the opposite being the case if setup was during a low pressure period.

Step 5: Using the Data

Over several hours and forthcoming days make a note of the level using the scale on the ruler.

Against each value make a note of the actual weather condition by direct observation of the weather.

Over a period of time this will begin to develop a picture of how the atmospheric pressure varies with the weather conditions.

Then by comparing the day to day variations you will be able to determine the most probable forthcoming weather.

The variation in the level from high the low pressure due to changing weather conditions should be clearly noticeable being over several centimetres.

If you log the value of the wafer level on the ruler and give the corresponding observable weather conditions a number you can then plot the comparative data in a spreadsheet and produce plots of the data.

It would also be useful to log the temperature as this has an effect on the value due to thermal expansion.

Happy weather watching.

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