jQuery cant select html tags that appended by jQuery?

jQuery cant select html tags that appended by jQuery?

  2. <!DOCTYPE html> 
  3. <html> 
  4. <head><script src=js/jquery-1.4.2.min.js></script></head> 
  5. <body>
  6. <span id="add">Click to add button</span>
  7. <div id="content">
  8. </div>
  9. <input name="outside" type="button" value="original">

  11. <script>
  12. $("body input[type=button]").click(function()
  13. { alert('YES!!');
  14. });

  16. $("body > #add").click(function()
  17. { $("body > #content").append("<input type=\"button\" value=\"created with jquery\">");
  18. });
  19. </script> 
  20. </body> 
  21. </html> 
When we click on the "original" button,it pops out a message,but the "created with jquery" button that created by clicking "Click to add button" doesn't pop out any message box.

Could someone tell me how to fix it?