Mercury barometer

A mercury barometer balances the weight of mercury in a glass tube against the atmospheric pressure above a reservoir of mercury at its base to provide a measurement of atmospheric pressure.

This weather instrument works like a set of scales to forecast the weather. A classic mercury barometer is constructed from a 3-foot glass tube that is open at one end and sealed at the opposite end. The glass tube is filled with liquid mercury and rests upside-down in a reservoir of mercury.

As the mercury moves down the glass tube, a vacuum is created. When the atmospheric pressure above the reservoir increases, the mercury inside the tube rises. As atmospheric pressure decreases the mercury moves down the tube, into the reservoir. This type of barometer was first constructed in by Evangelista Torricelli. The change in the mercury level in the glass tube is equal to the pressure exerted by the air above the reservoir and is measured using the scale marked on the glass tube.

Changes in atmospheric pressure occur prior to weather changes. Sudden drops in atmospheric pressure indicate stormy weather, while sudden rises in pressure predicate brief periods of fair weather. Gradual increases and decreases in atmospheric pressure point to a more sustained weather pattern. How Do Mercury Barometers Work?

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More From Reference.Barometerdevice used to measure atmospheric pressure. Because atmospheric pressure changes with distance above or below sea levela barometer can also be used to measure altitude.

There are two main types of barometers: mercury and aneroid. In the mercury barometeratmospheric pressure balances a column of mercury, the height of which can be precisely measured. To increase their accuracy, mercury barometers are often corrected for ambient temperature and the local value of gravity. Common pressure units include pounds per square inch; dynes per square centimetre; newtons per square metre the SI unit called the pascal ; inches, centimetres, or millimetres of mercury; and millibars 1 millibar equals 1, dynes per square centimetrepascals, or 0.

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Atmospheric pressure at sea level is about Of the many different varieties of mercury barometers, most variations arise from different techniques for measuring the height of the mercury column.

Though other liquids can be used in a barometer, mercury is the most common. Its density allows the vertical column of the barometer to be of manageable size. If water were used, for instance, the column would have to be 34 feet high. A nonliquid barometer called the aneroid barometer is widely used in portable instruments and in aircraft altimeters because of its smaller size and convenience.

It contains a flexible-walled evacuated capsule, the wall of which deflects with changes in atmospheric pressure. This deflection is coupled mechanically to an indicating needle. A mercury barometer is used to calibrate and check aneroid barometers. Calibration can be, for example, in terms of atmospheric pressure or altitude above sea level. The concept of altitude above sea level, based on barometric pressure, is used to create one type of aircraft altimeter.

A barometer that mechanically records changes in barometric pressure over time is called a barograph. Though mercury barographs have been made, aneroid barographs are much more common. The motion of the aneroid capsule is magnified through levers to drive a recording pen. The pen traces a line on a graph that is usually wrapped around a cylinder driven by a clockwork mechanism.

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Britannica Quiz. Inventors and Inventions. Which group invented and developed the early Internet? An overview of atmospheric pressure and the development of the barometer. Get exclusive access to content from our First Edition with your subscription. Subscribe today.A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughspressure systems and frontal boundaries.

Barometers and pressure altimeters the most basic and common type of altimeter are essentially the same instrument, but used for different purposes. An altimeter is intended to be used at different levels matching the corresponding atmospheric pressure to the altitudewhile a barometer is kept at the same level and measures subtle pressure changes caused by weather and elements of weather. The average atmospheric pressure on the earth's surface varies between and hPa mbar.

The average atmospheric pressure at sea level is hPa mbar.

mercury barometer

Although Evangelista Torricelli is universally credited with inventing the barometer in[1] [2] [3] historical documentation also suggests Gasparo Bertian Italian mathematician and astronomer, unintentionally built a water barometer sometime between and On 27 JulyGiovanni Battista Baliani wrote a letter to Galileo Galilei explaining an experiment he had made in which a siphonled over a hill about twenty-one meters high, failed to work. Galileo responded with an explanation of the phenomenon: he proposed that it was the power of a vacuum that held the water up, and at a certain height the amount of water simply became too much and the force could not hold any more, like a cord that can support only so much weight.

Galileo's ideas reached Rome in December in his Discorsi. Raffaele Magiotti and Gasparo Berti were excited by these ideas, and decided to seek a better way to attempt to produce a vacuum other than with a siphon. Four accounts of Berti's experiment exist, but a simple model of his experiment consisted of filling with water a long tube that had both ends plugged, then standing the tube in a basin already full of water.

The bottom end of the tube was opened, and water that had been inside of it poured out into the basin. However, only part of the water in the tube flowed out, and the level of the water inside the tube stayed at an exact level, which happened to be What was most important about this experiment was that the lowering water had left a space above it in the tube which had no intermediate contact with air to fill it up.

How Do Mercury Barometers Work?

This seemed to suggest the possibility of a vacuum existing in the space above the water. Torricelli, a friend and student of Galileo, interpreted the results of the experiments in a novel way. He proposed that the weight of the atmosphere, not an attracting force of the vacuum, held the water in the tube.

In a letter to Michelangelo Ricci in concerning the experiments, he wrote:. Many have said that a vacuum does not exist, others that it does exist in spite of the repugnance of nature and with difficulty; I know of no one who has said that it exists without difficulty and without a resistance from nature.

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I argued thus: If there can be found a manifest cause from which the resistance can be derived which is felt if we try to make a vacuum, it seems to me foolish to try to attribute to vacuum those operations which follow evidently from some other cause; and so by making some very easy calculations, I found that the cause assigned by me that is, the weight of the atmosphere ought by itself alone to offer a greater resistance than it does when we try to produce a vacuum.

It was traditionally thought especially by the Aristotelians that the air did not have weight: that is, that the kilometers of air above the surface did not exert any weight on the bodies below it.

Even Galileo had accepted the weightlessness of air as a simple truth. Torricelli questioned that assumption, and instead proposed that air had weight and that it was the latter not the attracting force of the vacuum which held or rather, pushed up the column of water. He thought that the level the water stayed at c. In other words, he viewed the barometer as a balance, an instrument for measurement as opposed to merely being an instrument to create a vacuumand because he was the first to view it this way, he is traditionally considered the inventor of the barometer in the sense in which we now use the term.

Because of rumors circulating in Torricelli's gossipy Italian neighbourhood, which included that he was engaged in some form of sorcery or witchcraft, Torricelli realized he had to keep his experiment secret to avoid the risk of being arrested. He needed to use a liquid that was heavier than water, and from his previous association and suggestions by Galileo, he deduced by using mercurya shorter tube could be used.

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InBlaise Pascal along with Pierre Petithad repeated and perfected Torricelli's experiment after hearing about it from Marin Mersennewho himself had been shown the experiment by Torricelli toward the end of Pascal further devised an experiment to test the Aristotelian proposition that it was vapours from the liquid that filled the space in a barometer.

His experiment compared water with wine, and since the latter was considered more "spiritous", the Aristotelians expected the wine to stand lower since more vapours would mean more pushing down on the liquid column.

Pascal performed the experiment publicly, inviting the Aristotelians to predict the outcome beforehand.A mercury barometer is basically just a scale that measures the weight of the atmosphere above. Easily the most impressive seesaw teeter totter that I've ever seen source of this image. If you understand how this works you'll be able to figure out how mercury barometers function.

You can't use an ordinary pan balance to weight the atmosphere because air is pushing down on both sides. A U-shaped tube filled with some kind of liquid that can slosh back and forth would work. Such an instrument is called a manometer and is often filled with mercury. To turn the manometer into a true barometer, we'll extend the tube on the right and close the top so that air isn't pushing down on the mercury.

We'll also use somewhat larger cylindrical columns of air and mercury that completely fill the insides of the tube. The weight of a very tall cylindrical column of air is balanced by a much shorter cylindrical column of mercury. The height of the mercury column will change as air pressure varies.

mercury barometer

Mercury is a liquid. You need a liquid that can slosh back and forth in response to changes in air pressure. Mercury is also very dense which means the barometer won't need to be as tall as if you used something like water.

A water barometer would need to be over 30 feet tall. With mercury you will need only a 30 inch tall column to balance the weight of the atmosphere at sea level under normal conditions remember the 30 inches of mercury pressure units mentioned earlier.

Mercury also has a low rate of evaporation so you don't have much mercury gas at the top of the right tube there's some gas, it doesn't produce much pressure, but it would be hazardous you if you were to start to breath it.

A barometer is essentially a balance. The weight of the atmosphere is balanced by the weight of a much shorter mercury column.A mercury barometer is a device that uses the various physical properties of mercury contained in a tube to measure barometric pressure, also known as air pressure or atmospheric pressure.

Changes in pressure are used to predict imminent weather changes, so barometers are useful tools for weather forecasting. When the barometric pressure drops, for example, it is possible that storms, rain, or wind are on the way. An increase in barometric pressure, on the other hand, could indicate that dry, fair weather could appear soon. Interpreting barometric readings can be quite accurate, but it is an imprecise science — there is no guarantee that the weather will act as expected.

There are two primary components to a mercury barometer: a mercury-filled tube that is closed on one end and a mercury reservoir.

mercury barometer

The tube of mercury is inverted in the reservoir so that the closed end faces up and the open end is partially submerged in the reservoir. Some of the mercury flows from the tube into the reservoir, creating a vacuum at the top of the closed end of the tube. The tube is generally about 3 feet 0. The height of the mercury in the tube changes with changing atmospheric pressure because the mercury in the reservoir is sensitive to these changes.

When the barometric pressure increases, force is applied to the surface of the mercury reservoir, forcing the level in the tube to increase. Conversely, when pressure drops, less force is applied and the level of mercury in the tube decreases.

The weight of the mercury in the tube, then, is balanced against the weight of the air above the reservoir. The markings on the side of the tube are used to measure the pressure levels as precisely as possible.

A mercury barometer is a commonly used tool in science, particularly in chemistry. There are many units used to measure pressure; for years, millimeters of mercury, or mm Hg, was the unit of choice. One millimeter of mercury is commonly referred to as one torr, after Evangelista Torricelli who invented this barometer.

One atmosphere is equal to Standard pressure is one atmosphere, or millimeters of mercury, and is the base pressure used in many scientific calculations.

Please enter the following code:. Login: Forgot password?Logistic Regressions Last Updated: Monday, 2017-10-30 10:31 A logistic regression is a supervised machine learning method for solving classification problems. You can create a logistic regression selecting which fields from your dataset you want to use as input fields (or predictors) and which categorical field you want to predict, the objective field.

Logistic regression seeks to learn the coefficient values b0, b1, b2. Xk must be numeric values. To adapt this model to all the datatypes that BigML supports, we apply the following transformations to the inputs:BigML.

You can also list all of your logistic regressions. Value is a map between field identifiers and a coding scheme for that field. See the Coding Categorical Fields for more details. If not specified, one numeric variable is created per categorical value, plus one for missing values. This can be used to change the names of the fields in the logistic regression with respect to the original names in the dataset or to tell BigML that certain fields should be preferred.

All the fields in the dataset Specifies the fields to be included as predictors in the logistic regression. If false, these predictors are not created, and rows containing missing numeric values are dropped. Example: false name optional String,default is dataset's name The name you want to give to the new logistic regression. Example: "my new logistic regression" normalize optional Boolean,default is false Whether to normalize feature vectors in training and predicting. The type of the field must be categorical.

The type of the fields must be categorical. The range of successive instances to build the logistic regression. Regularizing with respect to the l1 norm causes more coefficients to be zero, using the l2 norm forces the magnitudes of all coefficients towards zero.

Example: "l1" replacement optional Boolean,default is false Whether sampling should be performed with or without replacement. The minimum between that number and the total number of input rows will be used.

Example: 1000 tags optional Array of Strings A list of strings that help classify and index your logistic regression. By default, they are "one-hot" coded. That is, one numeric variable is created per categorical value, plus one for missing values. For a given instance, the variable corresponding to the instance's categorical value has its value set to 1, while the other variables are set to 0. Using the iris dataset as an example, we can express this coding scheme as the following table:The parameter value is an array where each element is a map describing the coding scheme to apply to a particular field, and containing the following keys:The value for coding determines which of the following methods is used to code the field: If multiple coding schemes are listed for a single field, then the coding closest to the end of the list is used.

Codings given for non-categorical variables are ignored. The dummy class will be the first by alphabetical order. This is because the default one-hot encoding produces collinearity effects which result in an ill-formed covariance matrix.

You can also use curl to customize a new logistic regression. Once a logistic regression has been successfully created it will have the following properties.

Mercury barometer

The coefficients output field is an array of pairs, one pair per class. The first element in the pair is a class value, and the second element is a nested array of coefficients for the logistic model that gives the probability of that class. Each inner array within the nested array contains the group of coefficients that pertain to a single input field. The class-coefficient pairs are listed in the same order as the class values in the objective field summary.

If the model was trained with missing values in the objective field, then a vector of coefficients will also be created for the missing class value, labeled with "", and listed last.

These are found under a field named stats. It is possible for null to appear among the values contained in stats. Wald test statistics cannot be computed for zero-value coefficients, and so their corresponding entries are null. Moreover, if the coefficients' information matrix is ill-conditioned, e.RamsMatchup -1 -110 1 -107 -1 -110 -1 -110 -1 -110 -1.

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mercury barometer

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