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propagation of waves or pulses, analogous to those of earth- 

 quakes, through solid materials. 



The experiments, of which this was a record, were con- 

 ducted during three years past, at Killiney Bay and on 

 Dalkey Island, off the Irish coast, and had for their object to 

 determine the rate at which a pulse produced by the explosion 

 of gunpowder, both in the discontinuous medium of the sand 

 of Killiney Bay, and in the nearly continuous one of the 

 granite of Dalkey Island, was propagated through these re- 

 spective solids for given distances. In the case of the sand, 

 the rate of transit might be presumed the slowest possible, in 

 that of the granite the fastest, due to any media forming con- 

 siderable portions of the earth's crust. Hence determinations 

 in these would give the limits of earthquake wave motion, 

 supposing such waves to be quite analogous to those experi- 

 mentally produced. 



The range chosen in the sand at Killiney Bay was a measured 

 half mile, and the powder used in each mine was twenty-five 

 pounds ; in the granite at Dalkey Island, the range was about 

 half this distance, and the charge for each mine, sunk in a 

 jumper-hole of twelve feet in depth, was from twelve to fifteen 

 pounds. The precautions taken for measuring both bases, the 

 peculiar arrangements for firing the mines by galvanic battery, 

 and for simultaneously releasing and stopping the chrono- 

 graphs, or instruments by which the interval of time of the 

 explosion from the moment of ignition, and that of the pulse 

 from its setting out to its arrival at the observer, were deter- 

 mined and registered, were minutely described; as also the 

 new instrument devised by the author, and called by him the 

 seismoscope, by which those minute and rapidly travelling 

 pulses were made visible to the eye, and capable of being dis- 

 tinctly observed. The transit rates, as thus determined, were 

 given, and compared with the recorded speed of earthquake 

 waves in some great earthquakes in India and elsewhere; 



