NEW ORLEANS, May 30th, 1874. On the 25th instant, the kind favor of the Western Union Telegraph Company enabled me to send to the Mayors of thirty-four large American cities the following dispatch: “By request of Relief Committee and leading citizens, I again call on American cities in behalf of fifty-four thousand victims of the great flood, for such aid as your prosperity may permit or your philanthropy prompt you to grant. Contributions in cash and provisions in thirty-five days have been les