Show Tricks of the Compass Exports say that the stool hull of a aASthe vessel M III rendered magnetic during construction lIy the hnmmorlng oC the metal and that every stool vessel has to hnvo Its I COlIlIIllSI1 COrreclotl In nun toract its own magnetic lines of force Tho magnetic Influence Is further com plented by the load carrIed by time vessel It tills load Is = magnetic or capable of being = The ore carrying vessels oC the grcnt lakes ex porlence grent lmculty on thlll account ac-count and tJll United States hdra graphic bureau Is endeavoring to teach pilots and captains or vessels i plyIng In this trade how to check their courso by moans oC the polorus Tho polorus Is an Instrument slml lar to the sun dial being Ilroldel with a gnomon and a gralluated arc on whIch a shadow oC the gnomon Is cast The Instrument Is set In n north and south direction 8S Inlllcated by the compass By noting the shadow on tho gradn ntd arc It Is bf a Possible to toll by com pnrlsoll with table furnished by the govornment just how far rom time north and south position the gnomon rpnlly lips thus showing the compass rror |