<script>
$(document).ready(function () {
/* Every time the window is scrolled ... */
$(window).scroll( function(){
/* Check the location of each desired element */
$('.box').each( function(i){
var bottom_of_object = $(this).position().top + $(this).scrollTop();
var bottom_of_window = $(window).scrollTop() + $(window).height();
/* If the object is completely visible in the window, fade it it */
if( bottom_of_window > bottom_of_object ){
$(this).animate({'opacity':'0.6'},500);
}
});
});
});
</script>