As a reader who's always found most historical novels about as convincing as fact-based TV movies, I'd never have tried one about 19th-century poet Gerard Manley Hopkins were it not for Ron Hansen (Mariette in Ecstasy), one of our best novelists. Exiles zeroes in on one short period of Hopkins' life circa 1875, when, as a Jesuit seminarian in Wales, he read about the death of five nuns in the sinking of a steamship and wrote what became a famous poem, ''The Wreck of the Deutschland.'' Hansen conveys a man conflicted by his callings as both a spiritual vessel and a full-blooded artist. A

