Names
- Monroe, James, 1758-1831.1
- Morgan, Lewis Henry, 1818-1881.1
- Morse, Samuel Finley Breese, 1791-1872.1
- Morton, William Thomas Green, 1819-1868.1
- Mount Washington Cog Railway.1
- Napier, Francis, Baron Napier and Ettrick, 1819-1898.1
- New York Elevated Railway Company.1
- Northern Pacific Railway Company.1
- O'Conor, Charles, 1804-1884.1
- Orr, James Lawrence, 1822-1873.1
- Palfrey, John Gorham, 1796-1881.1
- Parkhurst, Charles Henry, 1842-1933.1
- Parkman, Francis, 1823-1893.1
- Parks, Gorham, 1794-1877.1
- Paulding, James Kirke, 1778-1860.1
- Peabody, George, 1795-1869.1
- Pearce, Dutee Jerauld, 1789-1849.1
- Pearce, James Alfred, 1804-1862.1
- Pendleton, Edmund Henry, 1788-1862.1
- Pennsylvania Railroad.1