$.belowViewport = function(elem){
  var port = $(window).scrollTop() + $(window).height();
  return port <= $(elem).offset().top;
 }

 $.fn.onBecomeVisible = function( fn ){
  var obj = this;
  $(window).scroll( function() {
   obj.each( function() {
    if(!$.belowViewport(this) && !$(this).data('scrollEventFired')){
     $(this).data('scrollEventFired', true);
     fn(this);
    }
   });
  });
  return this;
 }

$('.elements:last').onBecomeVisible( function(elem){ loadNewElems(); } );