Photobarograph used at Radcliffe Observatory, Oxford

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

Originally the photobarographs were supplied with glass chimneys for their gas lamps, but following experiments at Kew Observatory some were replaced with copper chimneys, like this one.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.

The photobarograph was an instrument designed for meteorological observatories that enabled a continuous photographic record of air pressure to be taken.

A gas lamp provided a light source, and a system of lenses projected an image of the mercury surface of a cistern barometer onto the photographically sensitive paper around the recording drum. The drum was driven by clockwork, rotating once every 48 hours. A vertical shutter operated by the clock blocked the light for 4 minutes every two hours, leaving a time mark on the paper to aid the accurate reading of the records.

Since atmospheric temperature affected the height of the mercury column, the instrument also had a system that provided automatic temperature correction. Two zinc rods, one either side of the barometer, were fixed at their lower ends; when they expanded as the temperature rose they tilted a horizontal glass rod that set the base line traced onto the photographic paper.