Arrested- “Nemo,” the correspondent of the Pensacola Observer, was brought to this city on yesterday as prisoner of war, from Warrington. His real name is Mathews, and although he has written very interesting letters to the Observer, and is a secessionist of the deepest dye, he nevertheless managed to commit an indiscretion on last Friday, for which Gen. Bragg had him arrested as a prisoner of war, and brought to this city. It seems that the General contemplated making an attack on Fort Pickens on Friday night, and that he had managed to this effect admirably, when on Friday afternoon “Nemo’s” letter appeared in the Observer and blew all the fat in the fire. In this letter he stated the intention of Gen. Bragg, indirectly, and doubtless unintentionally. The Wyandotte happened at Pensacola on Friday afternoon, some of whose officers got hold of the paper, and communicated the information to Slemmer. We are unable to state what will be done with the prisoner. –Montgomery Confederation.