jquery mobile default font size

I have the following code:

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>jQuery Mobile</title>
<link rel="stylesheet" href="http://code.jquery.com/mobile/latest/jquery.mobile.css" />
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.js"></script>
<script src="http://code.jquery.com/mobile/latest/jquery.mobile.js"></script>
</head>
<body>

<div data-role="page" id="myPage">

    <div data-role="header">
        <h1>Header</h1>
    </div>
    <div data-role="content">Hello World!</div>
    <div data-role="footer">
        <h4>Footer</h4>
    </div>

</div>
<script src="/jQueryMatrix/Inc/js/PRINT.js"></script>
</body>
</html>

But my font size looks so small. It's true, I can zoom in, but shouldn't the default font size be legible?