//image rotation created on April 5, 2006 
 num=backgroundImage.length;
 incr=Math.floor(Math.random()*num);


function backgroundImageRotate()
{
 document.open();
 document.write("<div id='layerMast' style='background-image: url(http://www.cfa.ilstu.edu/images/levelThreeImages/"+backgroundImage[incr]+");'>");
 document.close();
}