// show/hide layers
		
function toggleLayer( whichLayer )
{
  var elem, vis;
  if( document.getElementById ) // this is the way the standards work
    elem = document.getElementById( whichLayer );
  else if( document.all ) // this is the way old msie versions work
      elem = document.all[whichLayer];
  else if( document.layers ) // this is the way nn4 works
    elem = document.layers[whichLayer];
  vis = elem.style;
  // if the style.display value is blank we try to figure it out here
  if(vis.display==''&&elem.offsetWidth!=undefined&&elem.offsetHeight!=undefined)
    vis.display = (elem.offsetWidth!=0&&elem.offsetHeight!=0)?'block':'none';
  vis.display = (vis.display==''||vis.display=='block')?'none':'block';
}

//show/hide layers end

// swap images
<!-- 

	if (document.images) {
		timeline_01_40s50s = new Image
		timeline_01_60s = new Image	
		timeline_02_60s = new Image
		timeline_02_70s = new Image	
		timeline_03_70s = new Image	
		timeline_04_70s = new Image	
		timeline_04_80s = new Image	
		timeline_05_80s = new Image	
		timeline_05_90s = new Image	
		
		timeline_image1 = new Image
		timeline_image2 = new Image
		timeline_image3 = new Image
		timeline_image4 = new Image
		timeline_image5 = new Image

		timeline_01_40s50s.src = "images/timeline/timeline_01_40s50s.gif"
		timeline_01_60s.src = "images/timeline/timeline_01_60s.gif"
		timeline_02_60s.src = "images/timeline/timeline_02_60s.gif"
		timeline_02_70s.src = "images/timeline/timeline_02_70s.gif"
		timeline_03_70s.src = "images/timeline/timeline_03_70s.gif"
		timeline_04_70s.src = "images/timeline/timeline_04_70s.gif"
		timeline_04_80s.src = "images/timeline/timeline_04_80s.gif"
		timeline_05_80s.src = "images/timeline/timeline_05_80s.gif"
		timeline_05_90s.src = "images/timeline/timeline_05_90s.gif"
		
		timeline_image1.src = "images/timeline/timeline_01_blank.gif"
		timeline_image2.src = "images/timeline/timeline_02_blank.gif"
		timeline_image3.src = "images/timeline/timeline_03_blank.gif"
		timeline_image4.src = "images/timeline/timeline_04_blank.gif"
		timeline_image5.src = "images/timeline/timeline_05_blank.gif"
			
		
	}
	
	function chgImg(imgField,newImg) {
		if (document.images) {
			document[imgField].src= eval(newImg + ".src")
		}
	}
		
// End hiding script from old browsers -->
// swap images ends