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XXVII. Account of Exjjerhnents made at Holyhead {North Wales) to ascertain the 
Transit-Velocity of Waves, analogous to Earthquake Waves, through the Local Mock 
Formations. My Eobekt Mallet, C.E., F.M.S. 
P.eceived June 18, — Eeacl June 20, 1861. 
Ix my “ Second Eeport on the Facts of Earthquake Phenomena” in the Eeport 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. 
The correctness of this view, and a general corroboration of the correctness of the 
experimental results themselves, have since been made known by the careful determina- 
tions by XbGGEEATii and Schmidt respectively, of the transit-velocities of actual earth- 
quake waves in the superficial formations of the Rhine country and of Hungary, and by 
myself in those of Southern Italy, all of which present low velocities coordinating readily 
with my previous experimental results. 
In the Eeport above mentioned, I suggested the desirableness of extending the expe- 
rimental determination of wave-transit to stratified and foliated rocks, as likely to pre- 
sent still lower velocities than those obtained for shattered granite, as well as other 
important or suggestive phenomena. The operations in progress at the Government 
quan-ies at Holyhead (Island of Anglesea, North Wales), of dislodging vast masses of 
rock by means of gunpowder for the formation of the Asylum Harbour there, appeared 
to me to present a favourable opportunity of making some experiments upon the 
MDCCCLXI. 4 u 
