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Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Science Museum Group
© The Board of Trustees of the Science Museum
Spectrograph designed by Gordon M. B. Dobson in 1924 and used by him at his home laboratory in Boars Hill, Oxfordshire for the measurement of atmospheric ozone. The instrument detected ultraviolet (UV) light reaching Earth’s surface from the Sun. Because ozone in the stratosphere absorbs UV wavelengths, UV intensity indicates ozone concentrations.
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.
Look closer
How was the ozone layer discovered?Details
- 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
- spectroscope
- spectrograph
- furnishing and equipment
- measuring device - instrument
- photometer
- credit:
- Dr. G.M.B. Dobson.
