// Slideshow class
function Slideshow(slideshow) {

    // method next()
    // changes the z order of the slides
    function next() {
        for (var i = 0; i < slides.length; i++) {
	    slides[i].style.zIndex = parseInt(slides[i].style.zIndex) + 1;
            if (slides[i].style.zIndex == slides.length) {
                slides[i].style.zIndex = 0;
            }
        }
    }

    // put document slide element references into a member array
    var nl = document.getElementById(slideshow).getElementsByTagName('div');
    slides = [];
    for (var i = 0; i < nl.length; i++) {
        slides.push(nl[i]);
        // initialize zIndex of slide
        slides[i].style.zIndex = i;
    }

    setInterval(next, 6000);
}