if (document.images) {            // Active Images
            circle1on = new Image();      
            circle1on.src = "images/circle1_on.jpg"; 
            circle2on = new Image(); 
            circle2on.src = "images/circle2_on.jpg";  
            circle3on = new Image();
            circle3on.src = "images/circle3_on.jpg";
            circle4on = new Image();
            circle4on.src = "images/circle4_on.jpg";
            
            circle1off = new Image();      
            circle1off.src = "images/circle_off.jpg"; 
            circle2off = new Image(); 
            circle2off.src = "images/circle_off.jpg";  
            circle3off = new Image();
            circle3off.src = "images/circle_off.jpg";
            circle4off = new Image();
            circle4off.src = "images/circle_off.jpg";
		}
		
// Function to 'activate' images.
         
function imgOn(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "on.src");
        }
}
         
// Function to 'deactivate' images.
         
function imgOff(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "off.src");
        }
}