The publicity-shy Mellons are, ironically, the subject of two family histories this spring, but neither is sufficiently searching or, on the other hand, diverting to make America's richest family public property. Hersh's is the hyperthyroid version. For six hundred pages it churns its subject-matter--the making, the apotheosis, the spending of the Mellon millions--into oracular/huckstering prose: ""Pure growth, what appetites--black holes of capital-absorbing antimatter. They could swallow everything; when financing hesitated the gagging was unbearable, the industrial earth shook. A.W. tittered: unruly creatures, but his. Could we deny them?"" This paragraph, be it known, has reference to the American economy in the mid-Twenties when Andrew Mellon was Secretary of the Treasury--the greatest since Alexander Hamilton, as platform orators put it, before the Depression and his own money-handling discredited him. But the more consequential the affairs here, the more difficult they are to construe; and insofar as Hersh is constantly attitudinizing--there is not a full, rounded, straightforward sentence in the book--it is impossible to know what to credit. One might suspect, for instance, that he is fairer than other biographers to Andrew Mellon's British wife Nora--whose estrangement from A.W. is the juiciest episode in Mellon family history--but with all flags flying, trumpets blaring, motors gunning full-time, who's to tell? ""Much the din obscured,"" indeed.