Edward Lillie Pearce, Charles Sumner. Memoir and Letters of Charles Sumner, Vol. III, 1845-1860. Boston: Roberts Brothers, 1894.
"March 26 . Wrote letters home ; visited the Invalides, and saw the new tomb of Napoleon ; then visited Mr. William B. Greene and his most intelligent wife, living off beyond the Luxembourg; saw something of that quarter ; then dined with Elliot C. Cowdin, a merchant here, once connected with the Mercantile Library Association [of Boston], — the first time I have met company at dinner for ten months ; then to the Italian opera, where I heard the last part of ' Il Barbiere di Siviglia.' " [page 530]
[another entry, p. 531, March 31, obscured in available copy, probably reads: "Din[ed with Mr. and Mrs.] Greene at their lodgings, beyond the Luxembourg.]