ON THE FACTS OF EARTHQUAKE PH^ENOMENA. 



277 



wire, diameter 16 Birmingham wire-gauge, flattened and screwed to each 

 side ; a fine platina wire streched between and soldered to both ; the diameter 

 of the platina wire that answered best was found to be such that 2 inches of 



Priming Cartridges, nearly half size. 

 Copper wire . / ^ ^,^^^ Ci^_ Copper wire. 



Diag. 4 



Copper wire. 



Paper cover. 



Diag. 5. 



PLATINA 

 WRAPPED WITH GUN COTTON 

 POWDER 



Paper. 



Longitudinal section. 

 it weighed 1*62 grain =0*01 4<75, or nearly ^^^th of an inch diameter, larger 

 wire requiring too much time and energy of battery to heat properly, and a 

 finer wire losing heat so rapidly by conduction as to be uncertain of firing 

 the powder. 



Taking the hint from this fact, it was found that the ignition was both 

 made certain and quickened by wrapping the wire round with gun-cotton, 

 whose bad conducting property and low temperature of ignition make it 

 valuable in the galvanic priming for common powder. This being done, the 

 hollow of the wood frame A was filled with fine glazed rifle powder, well-dried, 

 and then a piece of fine thin paper was pasted round over all. This priming 

 cartridge being inserted through the apertures in the ends of the canisters, 

 the copper wires extending out at each end, a perforated bung-cork was 

 slipped over one wire and secured in the neck of the canister, which was then 

 filled up with Dartford blasting powder ; the other bung was then inserted. 

 The two wires outside, each about 5 feet long, were now wrapped round 

 spirally with calico dipped in lac varnish, to insulate them ; and finally, the 

 bung-corks at each end were dipped into or coated with resinous cement, so 

 as to make the whole canister water-light. The wires being then coiled 

 loosely up, they were complete. 



I was indebted to Mr. Bergin of the Dublin and Kingstown Railway, for 

 the use of his powerful and convenient modification of Davison's galvanic 

 battery*, of which I had two troughs, consisting of six double cells each, 

 of cast iron and zinc elements. 



The cast-iron plates were immersed in strong commercial nitric acid mixed 

 with commercial sulphuric acid and placed in porous earthen troughs, and 

 opposed on each side by a zinc plate immersed outside the porous troughs in 

 commercial sulphuric acid diluted with water. The surface in action, when 

 this battery was in train, was for both sides of each cast-iron plate 168"75 

 square inches, and for the two opposed zinc surfaces S-t'SY square inches in 

 each element. It is unnecessary to enter into details here as to the very 

 convenient arrangements for uniting and disconnecting the plates. 



The igniting or deflagrating powers of this form of battery are enormous ; 



* See Lieut. Hutchinson's Mem. Prof. Pap. Roy. Eng., vol. vii. 



