nav_home = new Image();
nav_home.src = "images/nav_home_on.gif";

nav_about = new Image();
nav_about.src = "images/nav_about_on.gif";

nav_mission = new Image();
nav_mission.src = "images/nav_mission_on.gif";

nav_directions = new Image();
nav_directions.src = "images/nav_directions_on.gif";

nav_contact = new Image();
nav_contact.src = "images/nav_contact_on.gif";