var s = Snap("#svg"),
    circles = s.select("#circles"),
    c1 = circles.select('#c1'),
    c2 = circles.select('#c2'),
    c3 = circles.select('#c3'),
    c4 = circles.select('#c4'),
    position;

function animate(time) {
  position = Math.sin(Date.now()/600)*15+15;
  c1.attr({cx: 128 - position, cy: 128 - position});
  c2.attr({cx: 172 + position, cy: 128 - position});
  c3.attr({cx: 128 - position, cy: 172 + position});
  c4.attr({cx: 172 + position, cy: 172 + position});

  window.requestAnimationFrame(animate);

}

window.requestAnimationFrame(animate);