function reset() {
    $$('ul#gallery li').each(function(e) {
    	e.setStyle('opacity', 0);
    });
}
function animate() {
    reset();
    delay = 100;
    speed = 600;
    
    var i = 0; 
    var li = $$('ul#gallery li');
    li.each(function(e) {  
    	i += delay; 
    	setTimeout( function() {
    		e.set('tween', {duration: speed, transition: 'back:in'}).tween('opacity', 0, 1);
    	}, i);   
    });
}

window.addEvent('load', animate);