function showOver(id) {
  var img = document.images[id];
  if (img.well==null) preloadWell(img);
  img.src = img.well[1].src;
}

function showOut(id) {
  var img = document.images[id];
  img.src = img.well[0].src;
}

function preloadWell() {
  var img = preloadWell.arguments[0];
  img.well = new Array();
  img.well[0] = new Image();
  img.well[0].src = img.src;
  img.well[1] = new Image();
  img.well[1].src = "gfx/"+img.id+"1.png";
}