A History of Light & Colour Measurement: Science in the by Sean F. Johnston

By Sean F. Johnston

This can be a historical past of the hidden workings of actual technological know-how - a technical endeavour embedded in a social context. It argues that this 'undisciplined' topic, straddling academia, trade and rules, will be average not just of twentieth century technological know-how, yet of its destiny.

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Extra info for A History of Light & Colour Measurement: Science in the Shadows

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These three subjects, evaluated with distinctly different motives and techniques, were constructed along individualistic lines by a small number of investigators improbably convinced of the value and feasibility of intensity measurement. Only studies of radiant heat-a subject perceived as being more akin to thermal physics than to optics-adopted early the quantitative approach that was a more thoroughly integratedpart of its sub-culture. Colour seemed more amenable to a cataloguing or taxonomic strategy, a pragmatic solution to problems for which utilitarian considerations were paramount.

The reference in his case was therefore a definition of visual d i ~ t i n c t n e s s ~His ~ . method appears to have been shunned by serious investigators, however. Some of them argued that visual thresholding is limited by eye accommodation, and depends on background lighting, the rate of change of intensity, and the characteristics of the observer. One attempt to obviate the effect of eye A History of Light and Colour Measurement accommodation was to employ an aperture smaller than the smallest pupil diameter34.

As early as 1899, Karl Schwarzchild (1873-1916), then an observatory assistant in Vienna, developed techniques for combining spectroscopy with photographic photometry. These allowed the relative intensity of a star to be mapped as a function of wavelength, by applying the photometric method successively to narrow bands of wavelengths3'. From this colour information, experimentalists could classify stars by type, and theorists were able to estimate temperature31. Stellar classification, based on spectral lines and photometrically determined temperatures, became a major activity in astrophysics32.

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