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The instrument used a chlorine and bromine vapour filter to absorb visible light. A Féry prism and optical wedge produced a spectrum on a photographic plate. The intensity of spectral lines at ozone-absorbing UV wavelengths was measured relative to a reference wavelength unaffected by ozone.
University lecturer Gordon Dobson was fascinated with atmospheric ozone, supposing that its absorption of certain wavelengths of light would affect the circulation of the atmosphere. Recognising the need for regular ozone measurements to test these ideas, he built this spectrograph in 1924, and shortly afterwards five others to the same pattern. He found ozone concentrations fluctuated far more than had previously been supposed, varying daily, seasonally and also geographically.
By the late 1920s he had adapted the instrument’s design to use photoelectric cells rather than photographic plates.
During the mid-twentieth century Dobson’s spectrophotometers were despatched worldwide for ozone measurement, particularly during the International Geophysical Year of 1957-8. In 1985, dramatically declining ozone concentrations were recorded by a Dobson instrument in Antarctica; subsequent research confirmed the existence of an ozone ‘hole’ above the continent. This ultimately stimulated international action to ban ozone-destroying CFCs in industry.
Modern versions of Dobson’s instruments are still used to monitor stratospheric ozone today, in conjunction with other instruments both on the ground and on satellites.
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- Category:
- Meteorology
- Object Number:
- 1950-159
- Materials:
- aluminium alloy, brass (copper, zinc alloy), cotton (textile), glass, mahogany (wood) and wood (unidentified)
- Measurements:
-
component: 45 mm x 220 mm x 155 mm,
- type:
- ultraviolet spectrograph
- taxonomy:
-
- furnishing and equipment
- measuring device - instrument
- photometer
- furnishing and equipment
- measuring device - instrument
- spectroscope
- spectrograph
- credit:
- Dr. G.M.B. Dobson.
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