56 ANNUAL OF SCIENTIFIC DISCOVERY. 



from 125 to 130 cubic feet. When all were chambered out, a 

 board i):irtitiou was put up in front of each chamber to hold the 

 powder. Tlie greatest care was used in placing the powder in the 

 chambers; the men wore the French sabots, or bandaged their 

 feet in bagging ; the barrel of powder was opened at the moutii of 

 the tunnel, and carried into the chamber in sacks, the men grop- 

 ing their way into the (hirk tunnel, and delivering their danger- 

 ous burd(Mi to the foreman, wiio emptied it into one immense bin in 

 the chamber. At a certain stag^ of the filling up, 8 cartridges 

 were distributed at dilYerent points in the mass, each cartridge 

 having an electric wire leading to the central wire connected 

 with the machine outside. As fast as these chambers were filled, 

 they were sealed up with clay and the tunnel tamped with the 

 same material, the wires for firing the mass leading through a 

 small box at the bottom of the tunnel. These wires, two in num- 

 ber, were of copper, one an insulated wire to convey the elec- 

 tricity to the mass of powder, and the other a plain wire for the 

 return current; one connected with the positive, and the other 

 with the negative pole of a powerful " Beardslee " magnetico-elec- 

 tric machine, located in a secure place outside, and several feet 

 distant. On connecting the poles, the explosion took place with a 

 heavy, dull sound, and an immense mass of earth and rock was 

 thrown inio the air about 70 feet, and the whole face of the cliff 

 came crashing down to the base and tumbled into the sea. The 

 cliff has been blasted off for about 200 feet along its base and 

 tumbled into the sea, and about 17>5 feet in height with an aver- 

 age depth of about CO feet. — San Francisco paper. 



THE NEW THAMES TUNNEL. 



The way the tube tunnel is built is by means of 3 segments of 

 a circle of cast iron, each weighing 4 cwt., with a centre key- 

 piece at the top, weighing one cwt. Each segment or ring when 

 bolted together is only 18 inches long, but no fewer than 6 of 

 these rings are bolted ou in ever}' 2-i hours, so the tunnel is ad- 

 vancing at the rate of 9 feet a day. As the shi(»ld, which is 

 7 feet o inches in diameter, is pushed on for a length of 18 

 inches, it leaves within the tube or rim a space one inch greater 

 all round than that occupied b}' its own tube on the outside. 

 Tliis, therefore, leaves ample room to fit in the segments of 

 the tunnel-tube easily. This is done very rapidly. The bot- 

 tom segment is laid in its place, and the two siile segments 

 above it, and between these at the top the ke3'-piece is slid in. 

 Between the long horizontal flanges a layer of white pine is placed 

 before they are screwed close up. The spaces between the circular 

 flanges of each segment are regularly calked in with tow and 

 cement. Still, the shield on the cap is one inch wider all round 

 than the diameter of the tunnel tube within it, which comes after- 

 ward to occupy it, leaving an opening of that space between the 

 clay and iron. This interstice, when the segment ring is fix(;d, 

 is closed by pumping in blue lias cement, which, as it qnii-kly 

 sets, forms a ring of stone-work, preventing the action of the 



