if (document.images) {

var mnav1 = new Image();
mnav1.src = "/exhibitions/permanent/biodiversity/images/mnav_spectrum.gif";
var mnav1on = new Image();
mnav1on.src = "/exhibitions/permanent/biodiversity/images/mnav_spectrum_over.gif";

var mnav2 = new Image();
mnav2.src = "/exhibitions/permanent/biodiversity/images/mnav_rainforest.gif";
var mnav2on = new Image();
mnav2on.src = "/exhibitions/permanent/biodiversity/images/mnav_rainforest_over.gif";

var mnav3 = new Image();
mnav3.src = "/exhibitions/permanent/biodiversity/images/mnav_biosphere.gif";
var mnav3on = new Image();
mnav3on.src = "/exhibitions/permanent/biodiversity/images/mnav_biosphere_over.gif";

var mnav4 = new Image();
mnav4.src = "/exhibitions/permanent/biodiversity/images/mnav_solutions.gif";
var mnav4on = new Image();
mnav4on.src = "/exhibitions/permanent/biodiversity/images/mnav_solutions_over.gif";

var snav1 = new Image();
snav1.src = "/exhibitions/permanent/biodiversity/images/snav_spectrum.gif";
var snav1on = new Image();
snav1on.src = "/exhibitions/permanent/biodiversity/images/snav_spectrum_over.gif";

var snav2 = new Image();
snav2.src = "/exhibitions/permanent/biodiversity/images/snav_rainforest.gif";
var snav2on = new Image();
snav2on.src = "/exhibitions/permanent/biodiversity/images/snav_rainforest_over.gif";

var snav3 = new Image();
snav3.src = "/exhibitions/permanent/biodiversity/images/snav_biosphere.gif";
var snav3on = new Image();
snav3on.src = "/exhibitions/permanent/biodiversity/images/snav_biosphere_over.gif";

var snav4 = new Image();
snav4.src = "/exhibitions/permanent/biodiversity/images/snav_solutions.gif";
var snav4on = new Image();
snav4on.src = "/exhibitions/permanent/biodiversity/images/snav_solutions_over.gif";
}

function imgon(name)  {
if (document.images){
document[name].src = eval(name + "on.src");}
}

function imgoff(name)  {
if (document.images){
document[name].src = eval(name + ".src");}
}