| Summary: | This thesis is concerned with the cosmological evolution of quasars. I describe the construction of the Edinburgh Multicolour Survey from COSMOS scans of UK Schmidt photographic plates, taken in <I>UBVRI</I> wavebands at high galactic latitude in a contiguous area of 0.1 steradians (13 UK Schmidt fields). Two plates are taken close together in time in each waveband in each field so that spurious detections can be eliminated, and the errors on the measured magnitudes reduced. The raw COSMOS datasets were calibrated using photoelectric and CCD sequences in each waveband in each field. Systematic errors in the calibration due to "field effects" (variations in image size across each plate) are minimised by using the colours of the stars on each plate. Differences between the plates in each waveband are minimised. Differences in each waveband between fields are minimised by using the spatial distribution of stars in the survey, and requiring it to be uniform across the whole survey area. The calibration of the "worst" (as judged by the level of field effects) is tied in with that of the "best" plates. The final dataset is uniformly and accurately calibrated across the entire survey area. The systematic error in the COSMOS-measured magnitudes at <I>B</I> = 15 - 16 is 0.01<I>m</I>. The rms error at <I>B</I> = 17 - 18 (where most of the quasars are) is 0.09<I>m</I>. The Edinburgh Multicolour Survey was used to select a sample of bright UVX candidates. I then describe how follow-up spectroscopy was carried out to determine the nature of the candidates, and in the case of the quasars, to measure their redshifts. I compare the surface density of quasars found in this way to that measured by previous surveys, in particular the Palomar-Green Survey (Schmidt & Green 1983).
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