XXVII. Account of experiments made at Holyhead (North Wales) to ascertain the transit-velocity of waves, analogous to earthquake waves, through the local rock formations

In my “Second Report on the Facts of Earthquake Phenomena” in the Report of the British Association for 1851, the transit-velocities were experimentally determined of waves of impulse produced by the explosion of charges of gunpowder, and these velocities shown to be In wet sand . . . . . . 824.915 feet per second, In discontinuous granite . . 1306.425 feet per second, In more solid granite . . . 1664.574 feet per second, the range of sand employed having been that of Killiney Strand, and of granite that of Dalkey Island, both on the east coast of Ireland. These results produced some surprise on my own part as well as on that of others, —the transit-velocities obtained falling greatly below those which theory might have suggested as possible, based upon the modulus of elasticity of the material constituting the range in either case. I suggested as the explanation of the low velocities ascertained, that the media of the ranges (like all the solids constituting the crust of the earth) were not in fact united and homogeneous elastic solids, but an aggregation of solids more or less shattered, heterogeneous, and discontinuous, and that to the loss of vis viva, and of time, in the propagation of the wave from surface to surface, was due the extremely low velocities observed.