How to know if raphael object is hidden?

I am creating a diagram application in which I hide and show few elements e.g.

var c = paper.circle(10, 10, 10);
c.hide()

var c2 = paper.circle(10, 10, 10);
c2.show()

Now I want to act upon such shapes e.g. calculate bounding box etc but I am not able to find how to get if shape is hidden or not? Is there something like this shape.is_visible() or shape.attr('visible')