How do I make fade transition 'crossfade'?

I'm trying to get this to crossfade, but I'm not entirely sure how.

How can I make this jQuery method crossfade the images?

$('a.thumb').click(function () {
    var src = $(this).attr('href');
    if (src != $('div#imageDisplay > img').attr('src')) {
        $('div#imageDisplay > img').stop().animate({ opacity: '0', duration: 500 }, function () {
            $(this).attr('src', src);
        }).load(function () {
            $(this).stop().animate({ opacity: '1', duration: 500 });
        });
    }
    return false;
});