var screenImage = new Array("land","water","rock","night");
var count = screenImage.length;
var i = 0;


function scroll(){
	document.getElementById('swap').style.backgroundPosition = '0 -' + i + 'px';
	i = i+27;
	if (i >= 108){
		i=0;
		}
	setTimeout("scroll()", 2000);
	}