In the early fall of 1912, a blandly handsome, tousle-headed American schoolteacher arrived in London. Nearing 40, coming without introduction or much of a plan — except, as he later confessed, “to write and be poor” — he was making a last attempt to write himself into poetry. It would have taken mad willfulness to drag his wife and four children out of their settled New Hampshire life in a quixotic assault on the London literary scene. Still, he was soon spending a candlelit evening with Yeats in the poet’s curtained rooms, having come to the attention of that “stormy petrel” Ezra Pound, who lauded him in reviews back home. Little more than two years later, the schoolteacher sailed back, having published his first two books, “A Boy’s Will” (1913) and “North of Boston” (1914). He had become Robert Frost.