为什么点击没反应？

<html>
    <head>
        <title>Demo</title>
        <script type="text/javascript" src="jquery-1.4.2.min.js"></script>
        <script type="text/javascript">
            $(function(){//jquery开始 必不可少
                $("#button").click(function() { 
                     alert("I'm Test Button"); 
                 }); 
            })
            
        </script>
    </head>
 
    <body>
            <input type="button" value="测试" id="button" name="button">
    </body>
</html>