//smke effect	
var scrollSpeed = 50;       // Speed
var step = 1;               // Pixels to move per step
var current = 0;            
var imageHeight = 600;     
var divHeight = 300;     // How tall the divis.
//The pixel row where to start a new loop
var restartPosition = -(imageHeight - divHeight);
function scrollBg(){
    //Go to next pixel row.
    current -= step;
    //If at the end of the image, then go to the top.
    if (current == restartPosition){
        current = 0;
    }
    //Set the CSS of the header.
    $('#smoke').css("background-position","0 "+current+"px");
}
//Calls the scrolling function repeatedly
var init = setInterval("scrollBg()", scrollSpeed);