Diaries describe the attempts of Hallet to secure European and British patents and government orders for the diving bell, "Nautilus," and his interest in the financing of an American transcontinental railroad in London and Paris; and include information relating to George M. Dallas, minister to England, and John Y. Mason, minister to France, and lengthy commentaries on London society and British politics. Also, miscellaneous correspondence, bills, reports, leases, stock lists, clippings, and an invitation to the opening of the Union Pacific Railroad Eastern Division.