J. Duncan Campbell, American Military Insignia, 1800-1851
“ Almost every ray of the aura of sunlight can still be clearly seen; the North Pole is well marked with a vertical arrow; the Arctic Circle, Tropic of Capricorn, and the Equator are included on the half-globe, as are the meridians of longitude and the parallels of latitude; both North America and South America are shown, and that portion of North America east of the Mississippi basin is clearly denominated "United States." An unusual feature of the design is the way the arrows are held in the eagle's left talon—some of the arrow heads point inward, some outward. ”
