function newImage(arg) {
  if (document.images) {
    rslt = new Image();
    rslt.src = arg;
    return rslt;
  }
}

function changeImages() {
  if (document.images && (preloadFlag == true)) {
    for (var i=0; i<changeImages.arguments.length; i+=2) {
      document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
    }
  }
}

var preloadFlag = false;
function preloadImages() {
  if (document.images) {
    nav_note_over = newImage("/excerpts/tocqueville/nav-note-over.gif");
    nav_chapter_over = newImage("/excerpts/tocqueville/nav-chapter-over.gif");
    nav_map_over = newImage("/excerpts/tocqueville/nav-map-over.gif");
    nav_resources_over = newImage("/excerpts/tocqueville/nav-resources-over.gif");
    preloadFlag = true;
  }
}