function define(){
      var numpics = 8
      imageSource=new Array(numpics)
	for(i=0;i<numpics;++i)
	imageSource[i]=new Image()
	
    }

    function pre_load() {
      preload_image_01 = new Image()
      preload_image_01.src = "images/commercialA.jpg"
      preload_image_02 = new Image()
      preload_image_02.src="images/commercialB.jpg"
      preload_image_03 = new Image()
      preload_image_03.src="images/residentialA.jpg"
      preload_image_04 = new Image()
      preload_image_04.src="images/residentialB.jpg"
      preload_image_05 = new Image()
      preload_image_05.src="images/resourcesA.jpg"
      preload_image_06 = new Image()
      preload_image_06.src="images/resourcesB.jpg"
      preload_image_07 = new Image()
      preload_image_07.src="images/homeA.jpg"
      preload_image_08 = new Image()
      preload_image_08.src="images/homeB.jpg"
      
    }
    function initialize() {
      imageSource[0].src="images/commercialB.jpg"
      imageSource[0].name="commercial"
      imageSource[1].src="images/commercialA.jpg"
      imageSource[1].name="commercial_roll"
      imageSource[2].src="images/residentialB.jpg"
      imageSource[2].name="residential"
      imageSource[3].src="images/residentialA.jpg"
      imageSource[3].name="residential_roll"
      imageSource[4].src="images/resourcesB.jpg"
      imageSource[4].name="resources"
      imageSource[5].src="images/resourcesA.jpg"
      imageSource[5].name="resources_roll"
      imageSource[6].src="images/homeB.jpg"
      imageSource[6].name="home"
      imageSource[7].src="images/homeA.jpg"
      imageSource[7].name="home_roll"
      
    }

    define();
    pre_load();
    initialize();

    function SwapOutC() {
    document.commercial.src = imageSource[1].src;
    }

    function SwapBackC() {
    document.commercial.src = imageSource[0].src;
    }

    function SwapOutRd() {
    document.residential.src = imageSource[3].src;
    }

    function SwapBackRd() {
    document.residential.src = imageSource[2].src;
    }

    function SwapOutR() {
    document.resources.src = imageSource[5].src;
    }

    function SwapBackR() {
    document.resources.src = imageSource[4].src;
    }

    function SwapOutH() {
    document.home.src = imageSource[7].src;
    }

    function SwapBackH() {
    document.home.src = imageSource[6].src;
    }