如何让图片自动播放？

jQuery:

$(function(){
    function slideImg(i){
        var showWidth = $("#show").width();
        $("#slides li").stop().animate({left:-showWidth * i},400);
    }
    var _numList = $("#num li");
    _numList.mouseover(function(){
        var index = _numList.index(this);
        slideImg(index);
        $(this).addClass("current").siblings().removeClass("current");
    });
});

<div id="show">
    <ul id="slides">
        <li><img src="images/banner_1.jpg" width="980" height="450" /></li>
        <li><img src="images/banner_2.jpg" width="980" height="450" /></li>
        <li><img src="images/banner_3.jpg" width="980" height="450" /></li>
        <li><img src="images/banner_4.jpg" width="980" height="450" /></li>
        <li><img src="images/banner_5.jpg" width="980" height="450" /></li>
    </ul>
</div>
<ul id="num">
    <li class="current"></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
</ul>