jQuery: Hide and show paragraphs with hide() and show()

This is paragraph 1.

This is paragraph 2.

This is paragraph 3.

This is paragraph 4.

The Code START

  
  <script type="text/javascript" src="./jquery-1.5.1.js"></script>
  <script type="text/javascript">
      function hide() {
        $('p:first').hide();
      }

      function show() {
        $('p:first').show();
      }
    </script>
    </script>
  </head>

  <body>
  <h1>Hide and show paragraphs</h1>
  <div>
  <p>This is paragraph 1.</p>
  <p>This is paragraph 2.</p>
  <p>This is paragraph 3.</p>
  <p>This is paragraph 4.</p>
  </div>
  <form action="">
   <input type = "button" value="Hide paragraph" onclick="hide()"></input>
   <input type = "button" value="Show paragraph" onclick="show()"></input>
   
  </form>