LOUISVILLE, KY., March 22. Something of a sensation has been produced in the railroad postal service in this locality by the recent appointment of Hon. D. T. J. Mathews, of Mississippi, once a State Representative, and late a prominent attorney, to the position of Mail Agent between this city and Nashville. Mr. Mathews is a gentleman of highly dark color, and dresses to a Queen’s taste. He carries everything by storm, and cuts a fearful swell among the handlers of Uncle Sam’s mail-bags.