js不间断向下滚动代码

<dl id="marquee">
  <dt>
    <img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >
    <img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >
    <img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >    
<img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >
    <img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >
    <img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >
    <img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >    
<img src="http://net.wdsjz.com/UpFiles/Article/2011/1/12/2011011250804629.jpg" >  </dt>
  <dd></dd>
</dl>
 

<style type="text/css">
   h1 {
    font:400 16px/1 "Microsoft YaHei",KaiTi_GB2312,SimSun
  }
  #marquee {
    height:300px;
    width:200px;
    overflow:hidden;
    position:relative;
    border:10px solid #F2F1D7;
  }
  #marquee img {
    display:block;
  }
  #marquee dd {
    margin:0px;
    padding:0px;
  }
</style>
<script type="text/javascript">
  var Marquee = function(id){
    try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
    var container = document.getElementById(id),
    original = container.getElementsByTagName("dt")[0],
    clone = container.getElementsByTagName("dd")[0],
    speed = arguments[1] || 10;
    clone.innerHTML=original.innerHTML;
    container.scrollTop = clone.offsetTop;
    var rolling = function(){
      if(container.scrollTop == 0){
        container.scrollTop = clone.offsetTop;
      }else{
        container.scrollTop--;
      }
    }
    var timer = setInterval(rolling,speed)//设置定时器
    container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
    container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
  }
  window.onload = function(){
    Marquee("marquee");
  }
</script>