function impressum() {
	var width  = 500;
	var height = 330;
	var y = (screen.availHeight - height) /2;
	var x = (screen.availWidth - width) /2;
	var micro = window.open('impressum.html','impressum','resizable=0,scrollbars=yes,status=0,location=0,width='+width+',height='+height+', top='+y+',left='+x);
	micro.focus();
}