Back of the postcard. Some of the wording is not readable. It looks like the postcard was sent to a woman, Miss Stewart of California, from Paul Smith.
Back of photograph of Windsor Trowbridge, advertising for photography company "Ritz & Hastings." Reads:"Ritz & Hastings. 147 Tremont Street. Boston, Mass. Up one flight. Ernest F. Ritz. Geo. H. Hastings. Studeio connected by Elevator."