"CH represents the surface of the sea; BqH the sea bottom to the coast line through H; DK the lower surface of the solid crust. The lines, such as Opqr, are the directions of propagation of the wave at each point of those lines respectively, and show how the wave is refracted in passing out of one medium into another. The consecutive fronts of the wave are represented by the curved lines, which meet all the directions previously mentioned at right angles. It is supposed that, in these three media, the velocity of propagation is least in the water, greatest in the solid crust, and intermediate in the subjacent fluid."

HOPKINS, W.: On the Theories of Elevation and Earthquakes. Report of the Seventeenth Meeting of the British Association for the Advancement of Science. Held at Oxford in June 1847, London. John Murray 1848, p. 10.