A procedure is derived for obtaining low -resolution spectrophotometry of quasars directly from the objective -prism plates on which they were discovered. Measurements with a PDS microdensitometer of - 130 quasar candidates in approximately the central 19 square degrees of the UK Schmidt prism plate UJ3682P were used in the application of the procedure (practical details of the searches for quasars and of the objective -prism spectrophotometry are given). The success of the objective -prism spectrophotometry is demonstrated in a comparison with 12 slit spectra. Redshífts and equivalent widths can be determined with typical discrepancies of 1% and 40% respectively. This work on objective -prism spectrophotometry leads to a quantification of the selection effects that operate in the searches for emission-line objects on objective -prism plates. The quantification successfully explains an apparent discrepancy in the detection efficiencies of the CTIO-4m and Curtis Schmidt surveys for quasars. Spectra of quasars that were observed with the Image Photon Counting System on the Anglo- Australian Telescope are presented. The observations of quasars with broad absorption troughs indicate the ejection of matter with velocities up to ~ 22O00kms⁻¹ and with velocity dispersions up to - ~ 11000kms⁻¹. Data on the wavelength dependences of the contrast y and the grain response function g of the Kodak emulsion IIIaJ are presented.