National Geographic : 1939 Jul
AT HOME ON THE OCEANS A LIKE AN OVERSIZED BARNACLE, "IGDRASIL" CLINGS TO A CANAL TUG U. S. S. Favorite, used by the Panama Canal Commission, dwarfs the small yacht as together they make the downward trip through one of the locks. On the upward journey the craft was controlled by lines from shore. Electric locomotives, called "mules" in honor of their stubborn predecessors on the towpaths, pull ships through the locks. One "mule" appears just above the top of Igdrasil's mast.