Brass Barometer

A Little Information on the Barometer

A barometer measures air pressure: A "rising" barometer indicates increasing air pressure; a "falling" barometer indicates decreasing air pressure.

Who invented it?

About 1645, an Italian mathematician named Torricelli discovered the principle of the barometer by using a long glass tube closed at one end, which he put upside down in an open container holding liquid. He found that the pressure of the air bearing down on the liquid in the container forced it up the tube, and the measurement of the various lengths of the column of liquid was therefore a means of expressing the changes in air pressure. In order to have a tube of manageable length, the heaviest of all liquids, mercury, was later used.

For general use an easier though less precise means of measurement has been devised; the ANEROID BAROMETER (aneroid = without fluid).

Many people know from the weather charts displayed on television or published in the city newspapers, that highs and lows move in general from west to east, especially in the more southern latitudes. Bad weather is often associate with the lows, though moist onshore winds can cause rain in coastal areas even if the pressure is high. Your instrument will show whether pressure is rising or falling, that is, whether a high or low pressure system is approaching, or perhaps developing in intensity.

But here you have to be careful. Owing to a daily atmospheric tide effect, the pressure will normally fall by about three hectopascals between 9 am and 3 pm and will rise by a nearly similar amount between 3 pm and 9 am, even if weather systems are stationary. A smaller rise and fall occurs during the night and early morning. These daily (diurnal) changes must be allowed for before you can really say whether pressures are rising or falling due to weather systems. The best way to avoid this difficulty is to observe changes over 24-hour periods, using your movable set pointer. In other words, check your barometer at the same time each day.

When there is a fairly large fall, say more than seven hectopascals in 24 hours, you can assume that a high is moving away or that a depression is approaching or both.

OK,OK. Enough of the lessons! I'm not sure if many people actually know how a barometer works, or even care. If you care, perhaps you are now more educated than when you came to visit Nautical Decor...and more! That's a good thing. But many people just like to have one hanging on the wall because it is a beautiful instrument and often associated with nautical decor. Which is why we have it in our home. Why not put one on your wall too?

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