Facing the Flag by Jules Verne

Thomas Roch, a brilliant French inventor, has designed the Fulgurator, a weapon so powerful that the state which acquired it would become absolute master of earth and ocean. However, unable to sell his unproven idea to France or any other government, Roch begins to lose his sanity, becoming bitter, megalomaniacal and paranoid. The United States Government reacts by tucking him away at a luxurious asylum in New Bern, North Carolina, where he is visited by a notorious pirate of Malagasy origin.