You could follow it from there by looking at the empty spaces in a solid line of trees, the rootballs waving their witchy root toes in the air.

WSJ: Anna Quindlen on a Message Delivered by Tornado | House Call

This exploits one of the predictions of Einstein's general theory of relativity: that the path of a beam of light (which is a straight line in empty space) is bent inwards by the gravity of a massive object.

ECONOMIST: Cosmology: I spy with my little gravitational lens | The

The confidence of the home side was visibly growing, and Nicky Wroe even went for goal from the half-way line, punting a long range effort beyond the empty Burton goal with Deeney stranded.

BBC: Torquay 2-1 Burton

Each senator sits on three or four committees and even more subcommittees, most of which meet during the same morning hours, which helps explain why committee tables are often nearly empty, and why senators drifting into a hearing can barely sustain a coherent line of questioning.

NEWYORKER: The Empty Chamber