var preloadFlag = false;


  function newImage(arg) {	
  		if (document.images) {
	  		rslt = new Image();
	  		rslt.src = arg;
	  		return rslt;
  	}

  }

  function changeImages() {
  	if (document.images && (preloadFlag == true)) {
  		for (var i=0; i<changeImages.arguments.length; i+=2) {
  			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
  		}
  	}
  }
  
  function loadMastImages() {
	newImage('images/mast_off.gif');
	newImage('images/mast_on.gif');
	preloadFlag = true;
  }
  
  loadMastImages();