# “Book domino” propagation speed?

I was watching this video on the Guardian website. As it can be seen, the "wavefront" of the fallen books travel with a fairly constant speed, which I guess depends on the mass of the book $m$, on its height $h$, and of course on the spacing between two neighbour books $l$.

How would you estimate the "collapsing front speed" of the books?

$$v = \sqrt{gl}G(\frac{d}{l})$$
Where $g$ is the acceleration due to gravity, $d$ is the domino separation and $l$ is the domino height.
The function $G$ is given on page 8 of the article in terms of elliptic integrals.