if (document.images) {
  var butPHSn = new Image()
  butPHSn.src = "../images/menuBarPHS.gif"
  var butPHSa = new Image()
  butPHSa.src = "../images/menuBarPHSOn.gif"
  var butPESn = new Image()
  butPESn.src = "../images/menuBarPES.gif"
  var butPESa = new Image()
  butPESa.src = "../images/menuBarPESOn.gif"
  var butMESn = new Image()
  butMESn.src = "../images/menuBarMES.gif"
  var butMESa = new Image()
  butMESa.src = "../images/menuBarMESOn.gif"
  var butClustern = new Image()
  butClustern.src = "../images/menuBarCluster.gif"
  var butClustera = new Image()
  butClustera.src = "../images/menuBarClusterOn.gif"
}

function act(imgName) {
  if (document.images) 
    document[imgName].src = eval(imgName + 'a.src')
}

function inact(imgName) {
  if (document.images)
    document[imgName].src = eval(imgName + 'n.src')
}