var divs_to_fade = new Array('img1' , 'img2' , 'img3' , 'img4');
var i = 0;
var wait = 9000;
// the function that performs the fade
function swapFade() {
  $('#' + divs_to_fade[i]).fadeOut('slow');
  i++;
  if (i == divs_to_fade.length) i = 0;
  $('#' + divs_to_fade[i]).fadeIn('slow');
  setTimeout("swapFade()" , wait);
}

$(document).ready( function(){
  setTimeout("swapFade()" , wait);
});