help about animation

help about animation

hello, i wrote this jquery script but can't make it to work. This is a code:

    $(document).ready(function(){
        $('.menu-a1').hover(function(){$(this).animate(function(){$(this).css('background-image', 'url("images/Menu-first-hover.png")')}, 'slow');}
        , function(){$(this).animate(function(){$(this).css('background-image', 'url("images/Menu-first.png")')}, 'slow');});
    });