if (document.images) {
  image3on = new Image();
  image3on.src = "img/m1_02.gif";
  image4on = new Image();
  image4on.src = "img/m1_02.gif";
  image3off = new Image();
  image3off.src = "img/m0_02.gif";
  image4off = new Image();
  image4off.src = "img/m0_02.gif";


}

function turnOn(imageName) {
  if (document.images) {
    document[imageName].src = eval(imageName + "on.src");
  }
}

function turnOff(imageName) {
  if (document.images) {
    document[imageName].src = eval(imageName + "off.src");
  }
}