On scroll element appear. Use: $(this).scrollIn()

scrollIn.js

$.fn.scrollIn = function() {
    var $window = $(window),
        scrollTop = $window.scrollTop(),
        viewport = {
            top: scrollTop,
            bottom: scrollTop + $window.height()
        },
        bounds = this.offset();

    bounds.bottom = bounds.top + this.outerHeight();

    return (!(viewport.bottom < bounds.top || viewport.top > bounds.bottom));
};