var scrollSpeed = 70;       // Speed in milliseconds
var step = 1;               // How many pixels to move per step
var current = 0;            // The current pixel row
var imageWidth = 9999;     // Background image height
var headerHeight = 1000;     // How tall the header is.

//The pixel row where to start a new loop
var restartPosition = -(imageWidth - headerHeight);

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.
    $('#clouds').css("background-position","0 "+current+"px");


}

//Calls the scrolling function repeatedly
var init = setInterval("scrollBg()", scrollSpeed);