$.ajax({
			url: "log3.html",
			cache: false,
			success: function(html){
				$("#chatbox").html(html);

assuming you have the layout:
<div>
<p>line</p>
<p>line</p>
<p>line</p>
</div>

	setInterval (loadLog, 1500);	//Reload file every 2.5 seconds

<?php
	function tailFile($filepath, $lines = 1) {
		return trim(implode("", array_slice(file($filepath), -$lines)));
	}
?>

<?php
$file = file('log3.html');
echo $file[count($file) - 50];
echo $file[count($file) - 49];
echo $file[count($file) - 48];
echo $file[count($file) - 47];
echo $file[count($file) - 46];
echo $file[count($file) - 45];
echo $file[count($file) - 44];
echo $file[count($file) - 43];
echo $file[count($file) - 42];
echo $file[count($file) - 41];
echo $file[count($file) - 40];
echo $file[count($file) - 39];
echo $file[count($file) - 38];
echo $file[count($file) - 37];
echo $file[count($file) - 36];
echo $file[count($file) - 35];