It's Really Very Easy, And Only Requires Material You'll Find In Your Home
Make Your Own Water Barometer or Weather Glass
The Homemade Barometer Part 3
In Part 2 of this series on How To Make A Barometer,you'll find how to make a barometer (actually two barometers)in much the same way that Evangelista Torricelli did whenhe invented the barometer in 1643. We'll forget that the original invention came by accident while he was investigatingthe production of a vacuum. But such is often the way of science.
Torricelli's barometer was the model for all mercury based barometers for the next two centuries, and providedan easy, if not always convenient way of measuringair pressure.
But at much the same time, a more simple method became popularfor predicting changes in the weather. It was called theWeather or Storm Glass, and was used by sailors, farmers, and otherswho needed to know what the weather was doing. It was relativelycheap, consisiting only of blown glass, and using only water,sometimes with other additives.
The Weather Glass, also known as a Water Barometer,was quite useful, but was an indicator of weather changerather than a measurer of air pressure - it was almostimpossible to calibrate one with another, and was affectedby evaporation of the water. Nevertheless, weather glasseswere elegant instruments, and are still made today, mostlyas an ornament or talking point which actually does work.
Make Your Own Weather Glass
You will need a narrow necked bottle, a rubber stopper, a clear straw or piece of plastic tubing (the longer the better), some flexible window sealant, some water and some optional food coloring.
The hardest thing to do in the making of this device is to bore a hole through the centre of the rubber stopper and fit the straw or tube into it. It needs to be as airtight as possible, which is why we use rubber rather than cork.
Partly fill the bottle with water and food coloring - a little over half full. Insert the tube into the stopper and the stopper into the neck of the bottle. Make sure the end of the tube is below the water level. Now comes the fun part - blow a few bubbles into the water.
If everything has worked properly, after you've blown
some bubbles water should rise into the tube, hopefully
well above the top of the stopper. If not, check that
everything is airtight and try again.
Once you can see water in the tube a fair way above the
stopper, use the sealant or some other glue to prevent
any air leaking through the hole in the stopper or around
its edges. You can add a scale or a ruler beside the
tube to record changes in the water level.
What you've done here is slightly increase the air pressure
in the bottle by blowing air into it. The air can't get
back out, and the greater air pressure inside the bottle
will force water into the tube. Once the system has
stabilized, changes in atmospheric pressure will cause
the level of water in the tube to rise or fall. Increased
air pressure will make the liquid fall, decreases pressure
will cause it to rise - the opposite to the homemade
See if you can work out the reason for this - think about
which lot of water is directly in contact with the outside
One tip, which applies to all homemade barometers; try to
make your barometer on a day which is neither too wet and
stormy (low pressure) or sunny and still (high pressure)
If you pick a day when the air pressure is at about the
middle of its range, then the if the water starts at about
the middle of the tube it will have plenty of room to
move as the air pressure changes.
This simple barometer works the same way as the weather
glass, but the weather glass is a lot more elegant and
If you want to know more about Home Experiments Related
to Weather, just follow the link to an
excellent book, and I know from experience it's not just
for kids. And here are some other top introductory weather
And while most scientific attention was concentrated
on the mercury barometer, water based barometers like the
one described above were also in use, and in big numbers.
Follow the link to find out more about the Weather Glass.
But both of these barometers had their problems, not the
least of which was keeping the mercury or water in its container.
As technology improved, the better, more convenient Aneroid Barometer appeared, and that
is the most common form we see today.
You can also find information on
Setting and Calibrating Your Barometer, elsewhere in this
site, together with reviews of Modern Barometers.
This link will take you back to the Top, or, when you're ready, here's how to return to the Home page.
But just before you move on...
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