function newImage()
{

  images=new Array( 'action.png', 'gv.png', 'susy.png', 'correlator.png', 'toricSequence.png', 'tangentobstruction.png', 'lg.png', 'moment.png');
  var randomNumber = Math.floor(Math.random()*images.length);
  var bgimage = images[randomNumber];
  var bgsetting =  "url(\"http://www.math.upenn.edu/~guffin/images/rotation/"+ bgimage + "\")";
  var element = document.getElementById('logo');
  element.style.backgroundImage=bgsetting;
}