was already riddled by more than a hundred holes, varying from one inch to four and a half in diameter. The perforatrice—a simple-looking cylinder fixed in a square frame, and connected with a few pipes and stop-cocks—was placed in a fresh position in front of the rock, and, at a sign from the engineer, was set in motion. A boring-rod darted out like a flash of lightning, went with a crash against a new part of the rock, chipped out several fragments at a blow, and withdrew as quickly as it had advanced. Bang, bang, it went again with the noise of a gong. In ten seconds the head of the borer had eaten itself a hole; in a minute it had all but disappeared; in twelve it had drilled a hole nearly a yard deep, as cleanly as a carpenter could in a piece of wood. The rod not only moved backwards and forwards, and advanced as the hole grew deeper, but turned gently round the whole time; a jet of water, projected with great force, cooled the chisel, and washed out the hips. More air was turned on; the sound of the blows could no longer be distinguished one from another, they made a continuous rattle, and the rate was increased from two hundred to no less than three hundred and forty strokes per minute, or about half as fast again as the motion of the piston-rod of an ordinary express locomotive when going sixty miles an hour.
The pipes are seen which conduct the compressed air for the working of these boring-machines on approaching the tunnel-mouths. They are eight inches in diameter, and are supported by pillars of masonry. As these pipes, outside the tunnel, are exposed to constant variations of temperature-sometimes to as much as 54° Fahr. in a single day—it has been necessary to guard against their expansion and contraction. They have been fixed accordingly at stated intervals by means of iron rods, the lower ends of which are carried through the masonry and bolted to plates on the outside. The intermediate pipes are carried on rollers (d) on the tops of the pillars, and between each of the fixed points there is one pipe having an enlarged mouth—terminated by a cheek—which receives the end (a) of the ordinary pipe. A circular
