var img1 = new Array();
var img2 = new Array();
for ( i=1; i<=8; i++ ) {
	img1[i] = new Image();
	img2[i] = new Image();
	img1[i].src = './img/'+i+'.jpg';
	img2[i].src = './img/'+i+'a.jpg';
	var img = document.getElementById('im'+i);
	img.src = img1[i].src;
}
function on(num){
	var img = document.getElementById('im'+num);
	img.src = img2[num].src;
}
function off(num) {
	var img = document.getElementById('im'+num);
	img.src = img1[num].src;
}