$(document).ready(function() {
 // set opacity to nill on page load
    $("ul#menu span").css("opacity","0");
    // on mouse over
    $("ul#menu span").hover(function () {
      // animate opacity to full
      $(this).stop().animate({
        opacity: 1
      }, 'slow');
    },
    // on mouse out
    function () {
      // animate opacity to nill
      $(this).stop().animate({
        opacity: 0
      }, 'slow');
      });
});