Barometer
[1][3] French scientist and philosopher René Descartes described the design of an experiment to determine atmospheric pressure as early as 1631, but there is no evidence that he built a working barometer at that time.
[1] On 27 July 1630, Giovanni Battista Baliani wrote a letter to Galileo Galilei explaining an experiment he had made in which a siphon, led over a hill about 21 m high, failed to work.
[7] Physicists Gasparo Berti and father Raffaello Magiotti were excited by these ideas, and decided to seek a better way to attempt to produce a vacuum other than with a siphon.
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.
He needed to use a liquid that was heavier than water, and from his previous association and suggestions by Galileo, he deduced that by using mercury, a shorter tube could be used.
Pascal further devised an experiment to test the Aristotelian proposition that it was vapours from the liquid that filled the space in a barometer.
If, as suspected by mechanical philosophers like Torricelli and Pascal, air had weight, the pressure would be less at higher altitudes.
Therefore, Pascal wrote to his brother-in-law, Florin Perier, who lived near a mountain called the Puy de Dôme, asking him to perform a crucial experiment.
Perier was to take a barometer up the Puy de Dôme and make measurements along the way of the height of the column of mercury.
In September 1648, Perier carefully and meticulously carried out the experiment, and found that Pascal's predictions had been correct.
[11][12] The weather ball barometer consists of a glass container with a sealed body, half filled with water.
[13] A mercury barometer is an instrument used to measure atmospheric pressure in a certain location and has a vertical glass tube closed at the top sitting in an open mercury-filled basin at the bottom.
[14] Inspired by Torricelli, Otto von Guericke on 5 December 1660 found that air pressure was unusually low and predicted a storm, which occurred the next day.
Design changes to make the instrument more sensitive, simpler to read, and easier to transport resulted in variations such as the basin, siphon, wheel, cistern, Fortin, multiple folded, stereometric, and balance barometers.
Fortin barometers use a variable displacement mercury cistern, usually constructed with a thumbscrew pressing on a leather diaphragm bottom (V in the diagram).
A fine silken thread is attached to the float which passes up over a wheel and then back down to a counterweight (usually protected in another tube).
[19] Around 1810 the wheel barometer, which could be read from a great distance, became the first practical and commercial instrument favoured by farmers and the educated classes in the UK.
[20] From 1770 onwards, a large number of Italians came to England because they were accomplished glass blowers or instrument makers.
This expansion and contraction drives mechanical levers such that the tiny movements of the capsule are amplified and displayed on the face of the aneroid barometer.
Whereas the barometer displays the pressure on a dial, the barograph uses the small movements of the box to transmit by a system of levers to a recording arm that has at its extreme end either a scribe or a pen.
Commonly, the drum makes one revolution per day, per week, or per month, and the rotation rate can often be selected by the user.
Microelectromechanical systems (or MEMS) barometers are extremely small devices between 1 and 100 micrometres in size (0.001 to 0.1 mm).
[28] However, third party researchers were unable to confirm additional GPS accuracy or lock speed due to barometric readings.
[33] Localized high atmospheric pressure acts as a barrier to approaching weather systems, diverting their course.
Rapid pressure rises, such as in the wake of a cold front, are associated with improving weather conditions, such as clearing skies.
In the case of the Trimdon Grange colliery disaster of 1882 the mines inspector drew attention to the records and in the report stated "the conditions of atmosphere and temperature may be taken to have reached a dangerous point".
Aneroid barometers sold for domestic use typically have no compensation under the assumption that they will be used within a controlled room temperature range.
For example, if a barometer located at sea level and under fair weather conditions is moved to an altitude of 1,000 feet (305 m), about 1 inch of mercury (~35 hPa) must be added on to the reading.
Its dial is rotated so that the current atmospheric pressure from a known accurate and nearby barometer (such as the local weather station) is displayed.
In 1787, during a scientific expedition on Mont Blanc, De Saussure undertook research and executed physical experiments on the boiling point of water at different heights.
