The Magnetic Observatory at the Girard College, printed by P.S. Duval (c.1804-1886), 1847 (litho)

Plate illustrating an oblique elevation and floor plan of the Magnetic Observatory building, the first magnetic observatory in the United States, constructed on the west grounds of the college in 1839 after designs by Thomas Ustick Walter. Labels for instruments are included in the floor plan and include a transit; clock; dew point instrument; telescope declinometer; anemometer and rain gauge; barometer; telescope & horizontal force magnetometer; telescope & vertical force megnetometer; and thermometers. The brainchild of Alexander Dallas Bache (1806-67), the observatory was moved by master carpenter James O. Sawyer sometime after 1845 to the western ends of the college grounds and later ...