Barometer Planet » Mercury Barometer

The Fortin Barometer

admin — Tue, 29 Sep 2009 10:08:22 +0000

The Fortin barometer is a variation of the classic torricelli barometer working on the same principles as any other barometer but with a different construction. The one most notable difference between the two is that the Fortin barometer has the cistern made out of leather instead of metal like the aforementioned mercury barometer. The way the Fortin barometer works is different in a sense that it uses atmospheric pressure to balance the weight of a column of mercury against it. From that, any change in the atmospheric pressure is accompanied by an immediate change in the level of the mercury and can be measured against the scale engraved on the barometer. To be able to use the Fortin barometer in good measuring conditions you should aim for exposure spots where the temperature is uniform, the light is good and the Fortin barometer has a solid mounting both vertically and horizontally. As with any other liquid based barometer great care should be taken when transporting it from place to placn be.

The Fortin Barometer is mostly used for meteorological measurements whenever high accuracy and reliability are required. The Fortin barometer has been particularly designed for usage in meteorological land stations. Barometers are to be hung or mounted vertical, preferably on a solid wall, and require adequate exposure and accurate management.

Out of all the possible liquid based barometers the Fortin barometer is the most popular one offering great accuracy and reliability under the harshest weather conditions. The Fortin barometer is made out of a glass tube in which a tube of mercury is suspended making the cleaning process a bit more tricky. First you will need to place the Fortin barometer on a foam pad, cloth or cushion. The barometer’s delicate glass casing is fragile and may crack if it falls over during the cleaning process so special attention is required. Place the Fortin barometer in an upright position to keep the mercury from shifting from side to side. Lean the barometer against a steady surface, such as a wall and then wipe the barometer with a dry cloth to remove most loose surface dust and debris, use light pressure to avoid scratching the barometer’s glass casing with any bits of dust that are caught in the cloth. Finally you will need to wet a second piece of cloth until it’s damp to the touch. Spray the barometer with some glass cleaner, afterwards wipe it with the damp cloth and allow it to dry thoroughly before placing it back where it belongs.

fortin barometer

How to read a barometer

admin — Wed, 23 Sep 2009 09:20:07 +0000

The most important instrument used for weather forecasting is the barometer, but surprisingly only a handful of people know exactly how to read a barometer and interpret its measurements. A barometer does not only indicate present weather conditions but forecasts probable weather conditions 12 to 24 hours in advance.However it’s not that simple to read a barometer, taking into consideration the fact that the wind changes its direction constantly. A “rise” in barometric pressure must be considered in relation to the former reading and the same principle applies to a “fall”. In fact, a barometer is most useful if it is read only once a day, preferably at the same time of the day – 7-8am or 8-9pm are good times to do barometer readings – for reasons which we’ll get to later. Twice a day is also fine, but it’s really the 24 hour changes which are most significant for weather forecasters, so learning how to read a barometer is of great importance at this point. Sometimes the readings of the barometer can appear inaccurate saying that there is going to be rainy but in fact it’s going to be sunny. That happens because the weather we experience is caused by the interaction of air masses and pressure cells, which move fairly slow over the earth’s surface. Considering only air pressure varies, the extremes are high pressure cells and low pressure areas are the fronts, these two being the boundaries between different air masses. Between these extremes air pressure will vary fairly consistently, and we have a pressure gradient between the two extremes. So once the center of a low has passed, the pressure will gradually rise until the center of the following high passes through.

So when you read a barometer the needle will gradually rise up the scale from day to day. In most cases, a high pressure cell means calm, clear, sunny weather, and as the needle moves up the scale, the increase in pressure is suggesting fine, or “fair” weather is on the way. Similarly, as the high passes over the daily change in the needle’s position will show a decrease in the air pressure, and suggests that if this continues you will experience a period of low pressure. Of course, as in most things to do with weather and life, it’s not quite that simple to read a barometer, which means that although the pressure changes recorded by your barometer have some predictive value, they won’t always be right. For example, if the center of a high passes at a certain distance from where you’re located, you may not experience the fair weather that your barometer predicted before the pressure, and the needle begins to fall. Another general rule of thumb in “how to read a barometer” is that very high pressure readings may indicate windy conditions to follow. The reasoning behind this is that an extreme reading usually means a high pressure gradient to the next low, and high pressure gradients mean strong winds. This rule doesn’t apply in quite the same way to very low pressures. While the pressure gradient will certainly be high, the low is actually the focus of the winds, and unless you happen to be under the eye of a hurricane, the strong winds have already arrived. But you can, if you know how to read a barometer ,turn it into a very useful forecasting tool, but you will need to keep records of the weather to do so. Apart from pressure changes, you can record wind direction, wind direction changes, cloud cover and type of clouds, and the occurrences of rain, snow or thunderstorms.

So let’s recap on what you need to know about how to read a barometer:

Get a regular mercury barometer and start measuring the atmospheric pressure around you by simply measuring how high the mercury column goes up or down. The way you’re going to measure it is from bottom to top using a simpler ruler, keeping in mind that under regular atmospheric pressure the vacuum at the top of the barometer is at almost 30 inches (29.92 to be more precise). When the mercury column drops below that point, we’re experiencing a drop in atmospheric pressure and that means we’re going to get bad weather. This thing works viceversa as well so if the mercury column rises you can expect nicer weather. All in all learning how to read a barometer is a good thing if you’re an outdoor enthusiast and want to know how to plan your trips.

The Torricelli Barometer

admin — Tue, 22 Sep 2009 09:06:18 +0000

A barometer is an instrument that measures atmospheric pressure. Barometers are used by weather forecasters to measure air pressure, because rising or falling atmospheric pressure indicates a coming change in weather
Evangelista Torricelli was an Italian physicist. He was born in 1608 and died in 1647. He studied mathematics in Rome, and there became fascinated by the work of Galileo, whom he aided in the preparation of his Discorsi. Toriccelli succeeded Galileo, on the latter’s death, in the chair of philosophy and mathematics at Florence. Toriccelli is famous for balancing the weight of a column of mercury against the pressure of the atmosphere, the principle of the barometer. The space above the mercury in a brometer is still called the Torricellian vacuum.

The Torricelli barometer is made by first filling a dish with mercury which is afterwards poured into a long tube. The tube is filled almost to the top, stopped and inverted several times to remove air bubbles. The tube is then completely filled with mercury using a dropper. A finger is placed over the top of the tube and the tube is inverted and placed into the dish below the level of the mercury. When the finger is removed, the level of the mercury inside the tube drops until the pressure at the bottom of the column of mercury is equal to the pressure exerted by the surrounding air. Since no air was allowed to enter the tube, the empty space above the mercury column is a vacuum. We can measure the pressure exerted by the atmosphere by measuring how high the mercury column rises above the level of the mercury in the dish.
A safer way to fill the Torricelli barometer is to use a vacuum pump to create a vacuum at the top of the barometer. This draws the mercury up into the tube from the dish at the bottom. Continuing to draw a vacuum does not change the level of the mercury inside the tube. Closing the valve maintains the vacuum when the hose is removed.
Modern barometers measure air pressure in inches or millimeters of mercury or in units called bars and millibars. The bar is a unit of pressure in the metric system, and a millibar equals 1/1,000 bar. Scientists record most pressure measurements in millibars. The atmospheric pressure at sea level averages 1,013 millibars, which equals 29.92 inches (760 millimeters) of mercury. To compare measurements taken at various altitudes and temperatures, scientists first adjust them to the values that would be measured at sea level at 32°F (0°C). Torricelli also developed the concepts of momentum and impetus, and solved Fermat’s triangle problem for the Torricelli poin. All in all the Toriccelli barometer is an amazing tool used to measure atmospheric pressure. Toriccelli barometer also stands as the base of many modern barometers being a point of reference in our history.

toriccelli barometer

The mercury barometer explained

admin — Sat, 19 Sep 2009 11:19:12 +0000

The mercury barometer was first discovered by the Italian Evangelista Torricelli in 1643 and has been since then known as the Torricelli barometer. The principles on which the Torricelli aka the mercury barometer is based date since the time it was first discovered in the 17th century. Those principles although more than 300 years old are still the ones that stand at the base of a modern mercury barometer. By now you might be asking yourselves – so how does a mercury barometer work ? and I’m frankly glad you asked because we have the explanation ready.

How a mercury barometer works

The principles on which the barometer works can be easily illustrated as follows: take one long glass tube that is sealed at one end and then fill it with liquid mercury metal. Turn the filled tube upside down and place it in a bowl filled with mercury – also known as a cistern. When turning the tube upside down a bit of mercury will leak into the cistern and leave a vacuum at the top of the tube making our mercury barometer a real life example. What will happen next is that air pressure will start pushing down on the mercury in the cistern which will at its turn push up with an equal pressure on the mercury in the tube making the mercury in the tube go up or down, thus indicating the exact air pressure in the surrounding environment. Under normal circumstances, the column of mercury in the glass tube stands at a height of about 30 (29.92) inches (75 centimeters) when measured at sea level. An explanation of the above is pictured below for an easier understanding.

mercury barometer picture

So to recap here’s what you have to do to get a working mercury barometer: take one tube and fill it with liquid mercury, take a recipient – anything that resembles to a can and it’s water tight – and fill that one with liquid mercury as well. Turn the tube upside down and place it in the cistern. Wait 5 minutes and measure the height at which the mercury column stands in the tube and that’s the air pressure in the surroundings.

If you find barometers interesting you might want to consider purchasing a mercury barometer. There are various places where you can successfully buy mercury barometers at reasonable prices and in good standing. Ebay and Amazon are just a few of the big names where you could easily purchase an antique mercury barometer. A specialized place where you could also get more information on antique mercury barometers is Charles Edwin’s place where he showcases some of the nicest antique mercury barometers.

Although I don’t really emphasize on purchasing an used barometer because of the healthy risks they poses as a last alternative you could resort to this and purchase a used barometer and stay on the cheap side.