<div id="ch"></div>
                       
<script type="text/javascript">
var _oldHeight = $('#ch').height();

    $(document).ready(function(){
      refresh();
    });
 
    function refresh(){
        $('#ch').load('ch.php', function(){
           setTimeout(refresh, 1200);
		   if($(this).height() > _oldHeight){
         	$("#ch").animate({ scrollTop: $(this).height() }, "slow");
			_oldHeight = $(this).height();
		   }
  return false;
        });
    }
    
 
</script>