Fourth series of observations with a twenty-feet reflector : containing the places, descriptions, and measures of 1236 double stars (reduced to the beginning of 1830) : the greater part of them not previously described /by J.F.W. Herschel, Esq. M.A. Late fellow of St. John's College, Cambridge; F.R.S.L. and E., M.R.I.A., F.G.S., M.A.S., M.C.U.P.S.