The identity of Donne's "worthy friend F. H." is unknown to me. The letter
evidently belongs to the closing years of Donne's life. In printing this
letter, Mr. Gosse (_Life and Letters of John Donne, II, 254_) quotes from
Walton:
"The latter part of his life may be said to be a continued study; for
as he usually preached once a week, if not oftener, so after his
Sermon he never gave his eyes rest till he had chosen out a new Text,
and that night cast his Sermon into a forme, and his Text into
divisions; and the next day betook himself to consult the Fathers, and
so commit his meditations to his memory, which was excellent. But upon
Saturday he usually gave himself and his mind a rest from the weary
burthen of his week's meditations, and usually spent that day in
visitation of friends and other diversions of his thoughts; and would
say that _he gave both his body and mind that refreshment, that he
might be enabled to do the work of the day following, not faintly, but
with courage and cheerfulness_."