Cant get the fittext.js jquery plugin to work, anyone know why?

Code HTML4Strict:
<section class="content home">
	<a href="about.php" class="about">
		<h2 class="heading one">About</h2>
	</a>
	<a href="work.php" class="work">
		<h2 class="heading two">Work</h2>
	</a>
</section>
<section class="content home">
	<a href="blog.php" class="blog">
		<h2 class="heading three">Blog</h2>
	</a>
	<a href="contact.php" class="contact">
		<h2 class="heading four">Contact</h2>
	</a>
</section>
 
	<script src="http://code.jquery.com/ui/1.10.0/jquery-ui.js"></script>
	<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
 	<script src="js/jquery.fittext.js"></script>
	<script type="text/javascript">
		$(".heading").fitText();
	</script>
 
</body>
 
</html>

Code CSS:
section{
width: 100%;
}
 
a{
display: block;
float: left;
width: 50%;
}
 
        h2{
            width: 100%;
            text-transform: uppercase;
            display: block;
            text-align: left;
            line-height: 69%;
            font-size: 250px/1;
        }