NEW YORK — “Dear Mr. Lowell, I don’t know how to get in touch with you now that Randall is away but I should think this would reach you through Harcourt Brace. I just wanted to say….”

Three years ago, pregnant with twins and ordered to bed rest, playwright Sarah Ruhl got a present from a friend: “Words in Air,” the collected correspondence of poets Elizabeth Bishop and Robert Lowell. It is a behemoth of a book, three decades of epistolary conversation packed into 875 pages, beginning in 1947 with Bishop’s slightly tentative overture and lasting until Lowell’s death in 1977, when he was stricken with a heart attack in a New York City cab.