function myHeight() {
    if (document.all) 
        return document.body.offsetHeight;
    else if (document.layers)
        return document.body.document.height;        
    else
         return 6600;        
}

function myScroll() {
    window.scroll(0,documentYposition);    
    documentYposition += scrollAmount;
    if (documentYposition > documentLength)
        documentYposition = 0;
}

function start() {
    documentLength = myHeight();
    setInterval('myScroll()',scrollInterval);
}

var documentLength;
var scrollAmount = 1;    // scroll by 100 pixels each time
var scrollInterval = 60; // number of milliseconds between scrolls
var documentYposition = 0;