The History Of The Barometer

Part 1: The Mercury Barometer

The invention of the barometer came by accident - it was developed before it's present use was thought of. But before lookingat the invention of the barometer, here's a quick review ofwhat preceded the realisation that there was a connection betweenthe height of a column of mercury in a tube and changes in airpressure.

The barometer is the weather instrument used to measure air pressure, and in a previous article the question What Is Air Pressure? was raised.

The first clues to air pressure and its significance followed experiments by Evangelista Torricelli and others, whose primary aim was to create and investigate a vacuum.

This was achieved in a number of ways, but the easiest, if not the safest, was to invert a tube full of mercury into an open container of the same liquid, keeping the mouth of the tubebelow the level of mercury in the basin. Provided the tube was more than 30 inches, or 76cm long, a vacuum indeed formed inthe upper closed end. Apart from the lack of some form of measuring gauge, this was in fact a mercury barometer.

But back in 1643, nobody knew it yet.

Here's what happened next..... Back to Torricelli, and the Further History of the Barometer

Torricelli was a good scientist and a good observer, and he didn't stop thinking once he had found a simple way to form a vacuum.

Over time, Torricelli observed that the level of mercury in the tube varied a little from day to day, suggesting that air pressure varied. From there it wasn't such a big step to relate this to changes in the weather, and to some other surprising discoveries.

And so the barometer was born, although it wasn't until later that it was given that name. The next stages in the history of the barometer came quite quickly.

These discoveries stimulated a flurry of experiments, most notably by Blaise Pascal in France, who showed that air pressure fell with altitude. Robert Boyle in England, who in 1665 coined the name barometer, meaning weight measurer, suggested that a siphon arrangement using a tube bent in a U-shape would work just as well.

This was confirmed by Robert Hooke a few years later, and he also developed a lever arrangement which allowed the air pressure to be displayed on a dial. With further development, the dial displayed the pressure in inches of mercury.

This type of barometer, with its long neck and circular base, became known as the banjo barometer. It is still around today, although the dial is connected to a much more compact Aneroid Barometer, and the neck, instead of concealing a U tube full of mercury, acts as a support for a thermometer. Originals and replicas can be found at antique and specialist shops, while there are a large number of collectible Barometers at EBay.

An important advance in the use of the barometer for weather forecasting came as a result of the efforts of Robert Fitzroy during the 1850s and 60s. Fitzroy had risen to fame by being the Commander of HMS Beagle, in which Darwin made the trip that led to the development of evolutionary theory. Later he was promoted to Admiral in the British Navy, and was appointed Governor of New Zealand. On his retirement he became a member of Parliament and turned his attention to air pressure and the weather.

In 1862 he published his Weather Book, in which he summarized his immense weather knowledge by correlating weather changes with variations in air pressure observed in the barometer. He also developed the barometer which bears his name -the Admiral Fitzroy Barometer.

Although he probably died before it went into production, his barometer became, for a while, the standard weather forecasting instrument for weather watchers. It consisted of a mercury barometer, a thermometer, and a form of the Weather Glass or storm glass which reacted to air pressure and temperature changes, changes in humidity, and even changes in wind direction, although this may have been more wishful thinking than true science.

These elegant instruments are sometimes seen in auctions and antique shops, and replicas are also available, including at Amazon . But perhaps Fitzroy's longest lasting legacy is the traditional description of weather on today's barometers - sometimes resulting in more confusion than understanding. So much for the mercury barometer. They are still available today,and Mercury Barometers still have engineering and scientific uses. But they are expensive, difficult to move around, and retain all the problems with toxicity and safe disposal that come with mercury.

For the next 170 years or so, the mercury barometer became morepopular, more accurate and better designed, while the understandingof weather and the accuracy of predictions based on air pressureshowed some improvements. But the next real step in the historyof the barometer had to wait until other forms of technology hadimproved, and you'll find information on that in the pages on theAneroid Barometer.

Most scientific attention was concentrated on the mercury barometer,but water based barometers were still around, and in big numbers.They were known as a Weather Glass or Storm Glass. Follow the link to find out more about these elegant weather instruments.

You can also find information onSetting and Calibrating Your Barometer, and Homemade Barometers elsewhere in this site.

Another page worth a look covers things to keep in mind when Buying A Barometer.

And finally, if you're not quite sure just what those words and numbers on the dial of an aneroid barometer mean, here is a page on How To Use A Barometer. It's not as easy as you might think to use a home barometer for weather forecasting. 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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Last update 05/24/2011