if (document.images) {
   image23on = new Image();
   image23on.src = "images/coll_nav_sci_1.gif";
   
   image24on = new Image();
   image24on.src = "images/coll_nav_indig_1.gif";
   
   image25on = new Image();
   image25on.src = "images/coll_nav_ast_1.gif";
   
   image26on = new Image();
   image26on.src = "images/ttl_sub_coll_1.gif";
  
   image23off = new Image();
   image23off.src = "images/coll_nav_sci_0.gif";
   
   image24off = new Image();
   image24off.src = "images/coll_nav_indig_0.gif";
   
   image25off = new Image();
   image25off.src = "images/coll_nav_ast_0.gif";
   
   image26off = new Image();
   image26off.src = "images/ttl_sub_coll_0.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");
  }
}

// -->