Javascript 文本视差不工作

我使用jquery.parallax-1.1.3.js实现视差效果。地点：

问题：它适用于css背景位置。这适用于背景图像，但不适用于我的html中的文本

我想要的是：在这个js文件中添加一些代码，允许我在html文本H1、H2上使用视差效果。我更喜欢ID，所以H1周围会有一个div，ID和视差效果有关

这是js：

(function( $ ){
    var $window = $(window);
    var windowHeight = $window.height();

$window.resize(function () {
    windowHeight = $window.height();
});

$.fn.parallax = function(xpos, speedFactor, outerHeight) {
    var $this = $(this);
    var getHeight;
    var firstTop;
    var paddingTop = 0;

    //get the starting position of each element to have parallax applied to it      
    $this.each(function(){
        firstTop = $this.offset().top;
    });

    if (outerHeight) {
        getHeight = function(jqo) {
            return jqo.outerHeight(true);
        };
    } else {
        getHeight = function(jqo) {
            return jqo.height();
        };
    }

    // setup defaults if arguments aren't specified
    if (arguments.length < 1 || xpos === null) xpos = "50%";
    if (arguments.length < 2 || speedFactor === null) speedFactor = 0.1;
    if (arguments.length < 3 || outerHeight === null) outerHeight = true;

    // function to be called whenever the window is scrolled or resized
    function update(){
        var pos = $window.scrollTop();              

        $this.each(function(){
            var $element = $(this);
            var top = $element.offset().top;
            var height = getHeight($element);

            // Check if totally above or totally below viewport
            if (top + height < pos || top > pos + windowHeight) {
                return;
            }

            $this.css('backgroundPosition', xpos + " " + Math.round((firstTop - pos) * speedFactor) + "px");

        });
    }       

    $window.bind('scroll', update).resize(update);
    update();
};
})(jQuery);

以下是如何从html调用js：

    <script type="text/javascript" src="js/jquery.parallax-1.1.3.js"></script>
<script type="text/javascript">
$(document).ready(function(){

//.parallax(xPosition, speedFactor, outerHeight) options:
//xPosition - Horizontal position of the element
//inertia - speed to move relative to vertical scroll. Example: 0.1 is one tenth the speed of scrolling, 2 is twice the speed of scrolling
//outerHeight (true/false) - Whether or not jQuery should use it's outerHeight option to determine when a section is in the viewport
$('#third').parallax("50%", 0.5);

})
</script>

给一个div一个ID，给这个div一个背景图像。将ID连接到上面的视差效果。我想做同样的事情，但是用H1