document.observe('dom:loaded', function() {
    if($('flash')) {
        var fade = setTimeout("fadeout()", 3500);
        var hide = setTimeout("$('flash').hide()", 4800);
    }
});

                                                      
function fadeout(){
    new Effect.Opacity("flash", {
        duration: 1.0, 
        from: 1.0, 
        to: 0.0
    });
}