function openGallery() {
  var iwidth = 615;
  var iheight = 520;
  var il = screen.width/2 - iwidth/2;
  var it = screen.height/2 - iheight/2;
  var win = window.open("gallery.html",
                        "_blank",
                        "menubar=no,resizable=yes,top=" + it +
                        ",left=" + il + ",width=" + iwidth +
                        ",height=" + iheight + ",scrollbars=yes");
                        
}