IN explaining to British readers why the author of "The Scarlet Letter" suddenly found himself posted to Liverpool as American Consul, Henry James described in simplest terms the alchemy by which Washington converts domestic debts into foreign credits. When the party of Franklin Pierce came to power, "all good Democrats, in conformity to the beautiful and rational system under which the affairs of the Republic were carried on, began to open their windows to the golden sunshine of Presidential patronage." Hawthorne had been Pierce's classmate and campaign biographer, and although he was a more talented and sensitive observer than most of today's political appointees, he owes his post, as they do, to patronage pure and simple.