mercuryon= new Image();
mercuryon.src= 'img/mercury_nav_on.gif';
mercuryoff= new Image();
mercuryoff.src= 'img/mercury_nav_off.gif';
techon= new Image();
techon.src= 'img/merc_tech_on.gif';
techoff= new Image();
techoff.src= 'img/merc_tech_off.gif';
advon= new Image();
advon.src= 'img/merc_adv_on.gif';
advoff= new Image();
advoff.src= 'img/merc_adv_off.gif';