effect hide slide don't work with href

effect hide slide don't work with href


Hi,
I try to use jquery ui hide effect slide but it don't work after a
click on <a href="" >sign in</a>
it is ok if you delete the href. here is the code
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://
www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Signin</title>
    <title>Signin</title>
    <script src="http://code.jquery.com/jquery-latest.js"></script>
    <script type="text/javascript" src="./Resources/UI/
effects.core.js"></script>
<script type="text/javascript" src="./Resources/UI/
effects.slide.js"></script>
    <script type="text/javascript">
        $(document).ready(function() {
         $('#jform').show('slide', {direction:"down"},1000);
    $('a#signin').click(function() {
        $('#jform').hide('slide', {direction:"down"},1000);
    });
        });
    </script>
</head>
<body>
    <div id="jform">
        <a href="" id="signin">Sign in</a>
    </div>
</body>
</html>