Note 90 — Chapter XVII

I am afraid of becoming tiresome by going too far into the intricacies of this most difficult subject; but I say "towards the bottom of the hill," because, when a certain degree of verticality is reached, a counter protective influence begins to establish itself, the stones and waterfalls bounding away from the brow of the precipice into the air, and wearing it at the top only. Also it is evident that when the curvature falls into a vertical cliff, as often happens, the maximum of curvature must be somewhere above the brow of the cliff, as in the cliff itself it has again died into a straight line.