var speed = 4500;

function slideSwitch() 
{
  var $active = $('#slideshow div.active');
  if ( $active.length == 0 ) {
    $active = $('#slideshow div:last');
  }
  var $next = $active.next().length ? $active.next() : $('#slideshow div:first');
  $active.addClass('last-active');

  $next.css({opacity: 0.0})
    .addClass('active')
    .animate({opacity: 1.0}, 1000, function() {
      $active.removeClass('active last-active');
    });
}

$(function() {
  setInterval( "slideSwitch()", speed );
});