This is the fourth in a
series of papers which, as was explained in Papers I, II, and III (Lovell and
Hall 1970; Lovell and Hall 1971; Landis, Lovell, and Hall 1973), should be
helpful in understanding the changes in the light curve of β Lyrae. Betwen
March and October of 1972, 82 differential UBV observations were obtained by
Lovell and 107 by Landis.