<script type="text/javascript" src="jquery.js"></script>

                    <script type="text/javascript">
                    var auto_refresh = setInterval(
                    function(){
                    $('#message_display').load('show_messages_public.php');
                            }, 5000);
                    </script>

<?php
session_start();

function show_messages()
{
$mysql_host = "******";
$mysql_database = "*******";
$mysql_user = "*****";
$mysql_password = "*****";

$link= mysql_connect($mysql_host, $mysql_user, $mysql_password);

if (!$link) {
    die('could not connect:' . mysql_error());
}

$db_selected= mysql_select_db($mysql_database);

if (!$db_selected) {
    die('can't use' . $mysql_database . ':' . mysql_error());
}

$query= "SELECT * FROM public_chat ORDER BY time DESC LIMIT 2";
$result= mysql_query($query) or die(mysql_error());
while($row= mysql_fetch_array ($result)) {
    echo '<br/><font color="black">' .$row['time'] . "<br>" . '<b><big>' . '<font color="black">' . $row['user'] . ':' . '</big></b>' . " <br> " . $row['message'] .'</font>';
    echo "<br/><hr width="95%"<br/>"/*"<hr width="90%">"*/;
    }
}
?>

$('#message_display').load('show_messages_public.php?startInt=1&repeatTimes=5&incrementIncrease=3');

<?
    var startInt = $_GET['startInt'];
    var repeatTimes = $_GET['repeatTimes'];
    var incrementIncrease = $_GET['incrementIncrease'];

    var str = "";
    for (var i = startInt; i < repeatTimes * incrementIncrease + startInt; i += incrementIncrease) {
         str .= i."|";
    }

    echo str;
?>

setInterval(function() {
    $('#message_display').load('show_messages_public.php?callfunc=true');
}, 5000);

if ($_GET['callfunc'] == "true")
     show_messages();

$('#message_display').load('show_messages_public.php', {showmsg: 'public'});

switch($_POST['showmsg']) {
    case 'public':
        show_messages();
        break;
}

<?php
session_start();

$mysql_host = "******";
$mysql_database = "*******";
$mysql_user = "*****";
$mysql_password = "*****";

$link= mysql_connect($mysql_host, $mysql_user, $mysql_password);

if (!$link) {
    die('could not connect:' . mysql_error());
}

$db_selected= mysql_select_db($mysql_database);

if (!$db_selected) {
    die('can't use' . $mysql_database . ':' . mysql_error());
}

$query= "SELECT * FROM public_chat ORDER BY time DESC LIMIT 2";
$result= mysql_query($query) or die(mysql_error());
while($row= mysql_fetch_array ($result)) {
    echo '<br/><font color="black">' .$row['time'] . "<br>" . '<b><big>' . '<font color="black">' . $row['user'] . ':' . '</big></b>' . " <br> " . $row['message'] .'</font>';
    echo "<br/><hr width="95%"<br/>"/*"<hr width="90%">"*/;
}
?>