ON THE FACTS OF EARTHQUAKE PHENOMENA. 



283 



Section of cask and priming. 

 Diag. 7. 



Nine casks of powder were fired in all ; and this may be as convenient a 

 place as any other to describe the arrangements made for their ignition, &c. 

 Each cask held 25 lbs. weight of best Dartford, highly-glazed, coarse-grained 

 commercial blasting powder, and was prepared for firing in the following way. 

 The head of each cask was taken out by knocking off the hoops at one end. 

 Two holes were bored through the head at 4 inches apart, each hole half an 

 inch in diameter. Priming cartridges were made as already described for 

 the tin plate cartridges, but with longer wires. 



The ends of the two wires (which were brought parallel to each other at 

 a distance of 4 inches) were passed up throughh e holes in the loose head of 

 the cask, until the priming cartridge was a 

 foot or so below the head-piece ; half the pow- 

 der having been emptied out of the cask, the 

 priming cartridge was laid horizontally on 

 what remained, being then in the very centre 

 of the whole mass of powder ; the remainder 

 of the powder was now replaced in the cask, 

 pouring it over the priming cartridge, the 

 two wires being held up vertically ; the head 

 of the cask was now replaced, coopered up 

 and hooped, the wires projecting through the 

 holes in the head ; two pine-wood conical 

 plugs were now driven hard one into each 

 hole in the head, beside the copper wire, so 

 as to confine each in its own hole and keep 

 all strain off the priming cartridge. The wires 

 outside the cask were now insulated with 

 calico and lac varnish as before and coiled 

 up, and the casks were ready for firing, save 

 that before each was buried, the hoops on 

 the lower end only were nicked nearly through 

 with a saw, and all removed but two, so that 

 when the cask was buried standing on end with the firing wires uppermost 



description. Some heard a noise, others felt a shock, while still others both heard and felt 

 the effects of the explosion." — Times. 



Very much of the effect in transferring the shock of the explosion of powder to a distance 

 depends upon the sort of fulcrum upon which the explosion immediately acts. Thus I found, 

 by a rough experiment made in Kingstown Harbour, that a single pound of powder, in a flat 

 tin canister lying on the sand bottom, within about 60 feet of one of the granite piers and 

 under about 35 feet in depth of sea-water, when exploded, actually shook the whole mass of 

 the pier, or at least of the inner breast wall, on the coping of which we stood, so as to convey 

 the idea at the moment that the whole was founded on a quagmire or peat bog. This re- 

 markable effect I consider was due to the complete resistance afforded by the solid mass of 

 water above the focus, so that the whole force of the explosion was expended in shaking the 

 less homogeneous mass of the bottom on which the pier is built. 



As to the distance to which the sound of explosion has been heard through the air, or 

 through it and the earth in combination, the greatest on record is that of the tremendous 

 eruption of Sumbava in April 1815, when the subten-aneous noises were heard at Sumatra, 

 970 geographical miles away, and at Ternate, 720 geographical miles off, in the opposite di- 

 rection nearly (Raffles's ' Java') ; next to which is that of the reverberations of the volcano at 

 St. Vincent's, which are said to have been heard at Deraerara, a distance of 345 miles. 



The noise of the cannonade at the battle of Jena, in 1806, was heard as a low murmur in 

 the fields about Dresden, 92 miles away. It is almost certain that in this case the sound 

 was transmitted through the earth, for it was heard with perfect distinctness in the case- 

 mates of the fortifications, where the vaults acted as acoustic instruments to collect the 

 sound from the. earth and convey it to the ear. It was stated at the time, but on what au- 

 thority I cannot now say, that the cannonade at the siege of the Citadel of Antwerp, in 1832, 



