var wheel = function(event) { 
            var delta = 0; 
            if (!event)  
                event = window.event; 
            if (event.wheelDelta) { /* IE/Opera. */ 
                delta = event.wheelDelta / 120; 
            } else if (event.detail) { 
                 
                 
                delta = -event.detail / 3; 
            } 
             
            if (delta) 
                handle(delta); 
             
            if (event.preventDefault) 
                event.preventDefault(); 
            event.returnValue = false; 
        } 

         
        if (window.addEventListener) { 
             
            window.addEventListener('DOMMouseScroll', wheel, false); 
        } 
        /** IE/Opera. */ 
        window.onmousewheel = document.onmousewheel = wheel; 

        /** This is high-level function.
         * It must react to delta being more/less than zero.
         */ 
        var handle = function(delta) { 
            var random_num = Math.floor((Math.random() * 100) + 50); 
            if (delta < 0) { 
                // alert(" Mouse pulley scroll down: " + delta + " Times! "); // 1 
                $("btn_next_pic").onclick(random_num); 
                return; 
            } else { 
                // alert(" Mouse pulley scroll up: " + delta + " Times! "); // -1 
                $("btn_last_pic").onclick(random_num); 
                return; 
            } 
        }