请教图片移动问题
<table border="0" cellspacing="0" cellpadding="0" width="100%">
<tbody>
<tr>
<td height="27" width="89%">
<strong> 师资力量</strong>
</td>
</tr>
<tr>
<td bgcolor="#e44d92" height="1" colspan="2">
</td>
</tr>
<tr>
<td colspan="2">
<div style="width:900px; height: 138px; overflow: hidden" id="demo">
<table border="0" cellspacing="0" cellpadding="0" bgcolor="#ffffff"
height="138px">
<tbody>
<tr>
<td id="demo1">
<table border="0" cellspacing="0" cellpadding="0" bgcolor="#ffffff"
height="138px">
<tbody>
<tr>
<?php echo dt_picture(46,20,0,0,2);?>
</tr>
</tbody>
</table>
</td>
<td id="demo2" width="900"></td>
</tr>
</tbody>
</table>
</div>

<script>
var speed = 20
demo2.innerHTML = demo1.innerHTML
function Marquee1() {
if (demo2.offsetWidth - demo.scrollLeft <= 0)
demo.scrollLeft -= demo1.offsetWidth
else {
demo.scrollLeft++
}
}
var MyMar1 = setInterval(Marquee1, speed)
demo.onmouseover = function() { clearInterval(MyMar1) }
demo.onmouseout = function() { MyMar1 = setInterval(Marquee1, speed) }
</script>

</td>
</tr>
<tr>
<td colspan="2"> 

</td>
</tr>
</tbody>
</table>
<!-- end 师资力量-->

为什么图片移动一会就不移动了？？

[解决办法]
多显示点数据