Barographs are barometers with a writing arm that records pressure changes on rotating paper. They were once used by meteorologists and mariners, and provide insight into weather patterns. Early barometers were mercury-filled, but the introduction of the aneroid barometer in 1843 led to the development of the barograph. Most barographs have stacks of barometers and a roll of paper to record pressure changes. They are important for safe navigation at sea and antique models are prized for their craftsmanship. Modern barographs are digital.
A barograph is a barometer that has a writing arm that records the rises and falls in barometric pressure on a rotating roll of paper. Barographs were once the primary tool of meteorologists, mariners, and others who closely track pressure changes over time. The collection and study of the scrolls has provided insight into fronts, weather systems, and general atmospheric changes, and has enabled a record of these patterns to be kept for posterity. In the modern era, computerized discs and digital barographs have largely replaced self-recording versions, although early models are still prized for their craftsmanship.
Barometers have been around since at least the mid-1600s, but early models were pretty rudimentary. Most were mercury-filled capsules that fluctuated with atmospheric changes. To record weather patterns, barometer owners had to closely monitor the devices and diligently take notes. The introduction of the barograph in 1843 provided a more self-contained way of tracking barometric changes.
Barograph technology is based on the functionality of aneroid barometers. Aneroid barometers were some of the first so-called “advanced” barometers, because they did not depend on rising liquid, but rather on an aneroid capsule cell, which functions in many ways like an alloy battery. These barometers indicate pressure changes with a rotating dial synchronized with numbers on a flat face resembling a clock.
In a barograph, the central quadrant of the aneroid points outward, toward a roll of paper. Most of the time, the barometer isn’t big enough to reach the chart. For this reason, most barographs feature stacks of barometers, usually four to seven, depending on size. The upper barometer holds the recording arm.
A roll of barographic paper sits immediately adjacent to the barometer stack in most models. The reel spins slowly, usually powered by quartz clock movement, and the barometers are fixed. As the pressure changes and the arm moves, it leaves a mark on the paper.
The first barograph featured a sharp metal arm that recorded pressure by scratching a roll of film. More modern examples use markers on optimized graph paper to indicate the day, time, and related pressure measurement. Most barographic charts record an entire week at a time, although specifics vary from device to device.
Barographs have special importance at sea, where forecasting of weather patterns is often essential for safe navigation. Carrying a regular barograph on deck often proves problematic, however, because the ship’s constant motion distorts the device’s recording mechanism. For this reason a specific marine barograph was developed, where the recording device and the chart paper are both specially anchored and weighted to resist a large amount of surface movement.
Most of the recording barographs still on the market are antique models. The new barographs are almost exclusively digital, allowing scientists and forecasters to quickly digitize, amalgamate and compare stored graphs. The workmanship that is demonstrated in many of the original models was so precise that many of them still work perfectly and often command very high prices.
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