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We present the results of three years of ground-based observations of theSeyfert 1 galaxy NGC 5548, which combined with previously reported data, yieldoptical continuum and broad-line H-beta light curves for a total of eightyears. The light curves consist of over 800 points, with a typical spacing of afew days between observations. During this eight-year period, the nuclearcontinuum has varied by more than a factor of seven, and the H-beta emissionline has varied by a factor of nearly six. The H-beta emission line responds tocontinuum variations with a time delay or lag of 10-20 days, the precise valuevarying somewhat from year to year. We find some indications that the lagvaries with continuum flux in the sense that the lag is larger when the sourceis brighter.Comment: 29 pages, 6 figures. Accepted for publication in ApJ (1999 Jan 10

Steps toward Determination of the Size and Structure of the Broad‐Line Region in Active Galactic Nuclei. XV. Long‐Term Optical Monitoring of NGC 5548