need help with infinite scrolling

Question

i am trying to debug why when i use this infinite scrolling plugin, nothing happens ...

$(function() {
  $(".posts").infinitescroll({
    navSelector: "#pageNav",
    nextSelector: ".next",
    itemSelector: ".posts .post"
  });
});

<div class="posts">
  <div class="post">1. ...</div>
  <div class="post">2. ...</div>
  <div class="post">3. ...</div>
  <div class="post">4. ...</div>
  <div class="post">5. ...</div>
  <div class="post">6. ...</div>
  <div class="post">7. ...</div>
  <div class="post">8. ...</div>
  <div class="post">9. ...</div>
  <div class="post">10 ...</div>
</div>
<ul id="pageNav" class="clearfix">
  <li><a href="page1.html" class="active">1</a></li>
  <li><a href="page2.html" class="next">2</a></li>
  <li><a href="page3.html">3</a></li>
  <li><a href="page4.html">4</a></li>
  <li><a href="page5.html">5</a></li>
</ul>