Slow background scroll

HTML

<div class="content"></div>
<div class="content"></div>
<div class="content"></div>

CSS

body {
    background: url(http://www.hw.ac.uk/estate/images/landscape-images/historic-landscape-big.JPG) no-repeat fixed center 0 transparent;
}

.content {
    width: 200px;
    margin: 20px auto;
    height: 200px;
    background-color: #CCC;
    border: 2px dotted #F00;
}

JavaScript

document.addEventListener('scroll',function(e) {
    var newPos = (window.scrollY*-1)/10
    document.body.style.backgroundPosition = "center "+newPos+"px";
});