In urbane and cultured modulations, Dr. Green discusses the failure of the social structure of 19th century Boston to produce anything beyond what he believes is mediocre literature. 19th century Boston ""was not a product of continuity, so much as creativity,"" he tells us. Boston wanted to be great, wanted to be built on cultural values. It backed institutions and magazines; the leading families --Lowells, Adamses, Eliots, Cabots, Quincys--ran Harvard ""as trustees, as benefactors, as scholars."" Seeking prototypes to dissect, Dr. Green picks George Ticknor as representative of the first half-century and his nephew, Charles Eliot Norton, as son of the Gilded Age. Dr. Green finds that the tragedy of mediocrity sprang from that ""act of cowardice"" which excluded ""the telling of deeply personal truths."" Only the four aesthetes -- Henry James, Henry Adams, George Santayana, Bernard Berenson-- were ""first rate"" and they were exiles. Professor Green, formerly of Wellesley and Tufts, now of Birmingham University, however, never does explain exactly why gentility in the 19th century deteriorated into what we call Victorianism; why passion (intellectual and emotional) was barred from Fenway and other courts. This impatient failure to illuminate the crucial limits his lovely book as a basic text. Nevertheless it is an elegant joy to read. To miss it is sheer cultural self-deprivation.