Barograph

A barograph is a barometer that records the barometric pressure over time.

Alexander Cumming, a watchmaker and mechanic, has a claim to having made the first effective recording barograph in the 1760s using an aneroid cell. Cumming created a series of barometrical clocks, including one for King George III. However, this type of design fell out of favour. Since the amount of movement that can be generated by a single aneroid is minuscule, up to seven aneroids (so called Vidie-cans) are often stacked "in series" to amplify their motion. This type of barograph was invented in 1844 by the Frenchman Lucien Vidi (1805–1866).

In such barographs one or more aneroid cells act through a gear or lever train to drive a recording arm that has at its extreme end either a scribe or a pen. A scribe records on smoked foil while a pen records on paper using ink, held in a nib. The recording material is mounted on a cylindrical drum which is rotated slowly by clockwork. Commonly, the drum makes one revolution per day, per week, or per month and the rotation rate can often be selected by the user.

Various other types of barograph have also been invented. Karl Kreil described a machine in 1843 based on a syphon barometer, where a pencil marked a chart at uniform intervals.Francis Ronalds, the Honorary Director of the Kew Observatory, created the first successful barograph utilising photography in 1845. The changing height of the mercury in the barometer was recorded on a continuously moving photosensitive surface. By 1847, a sophisticated temperature-compensation mechanism was also employed. Ronalds’ barograph was utilised by the UK Meteorological Office for many years to assist in weather forecasting and the machines were supplied to numerous observatories around the world.

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