$.fn.rollByLine = function(millisec){
    this.each(function(){
        var $ul = $(this).children("ul");
        var offset = $ul.children("li").height();
        setInterval(function(){
            $ul.animate({"margin-top": "-" + offset + "px"},500,function(){
                $(this).children("li:first").appendTo($(this));
                $(this).css({"margin-top": 0});
            });
        },millisec);
    });
};