The steam frigate Niagara, which was em. ployed last year as one of the squadron in the unfortunate attempt to lay the above-named telegraph cable, is now at the Navy Yard, Brooklyn, undergoing a thorough overhauling inside and out. Her machinery is to be refitted, but we suppose no alterations are to be made in it. It is now reported that she is to be again employed in the second attempt next summer, to lay the cable, and the changes she is now undergoing are designed to place her in the most effective condition for that prospective event.