MEANS OF COMMUNICATION. 9 
at early date, for in Babylon an arched way 500 feet long, 15 feet wide, and 
6 feet high, passed under the bed of the Euphrates connecting the two 
palaces. The grotto of Pausilippo near Naples is also a structure of this 
kind. In modern times tuunels have been excavated in most civilized 
countries. In Germany we name the tunnel near Tiibingen in Wirtemberg, 
by means of which the river Ammer is carried through the Oesterberg ; 
also the tunnel near Reichenau in Austria, 1,362 feet long, and 3,700 feet 
above the level of the sea, through which a stream is made to pass for the 
purpose of floating wood to Vienna. In France the canal of Languedoc is 
carried through a mountain. Between Gravesend and Rochester in Eng- 
land is a tunnel of about two miles in length, through which passes a canal 
connecting the river Medway with the Thames. The Bridgewater canal 
passes through a tunnel near Manchester, and various other tunnels for 
similar purposes existin England. Of Railroad tunnels we shall speak below. 
The most remarkable tunnel is the celebrated Thames tunnel, of which 
we have given representations in pl. 1, jigs. 28-34. It was built by Sir I. 
Brunel, a French engineer, who on seeing a ship’s keel hollowed out entirely 
by the worm, had conceived the idea that a large tunnel might be made by 
driving a number of small tunnels close to each other. For this purpose he 
constructed his so-called shield, of which a single field is represented in jig. 
33. These fields, of which there are twelve in all, as jig. 31 shows, consist 
of the bottom-plates, 7, 7, the side-faces, d, composed of several pieces, and the 
top-plates, ce, ¢; each has three compartments, in each of which a man can 
work erect. The openings in the side-plates allow the workmen to assist 
each other. The forward face of the field is composed of a number of iron 
plates, a, a, 6 inches wide and 2 inches thick, each of which is supported by 
two screws against the side pieces, when the shield is placed against the 
earth wall that is to be perforated. The earth is thus sustained while the 
shield itself abuts at its head and foot plates against the masonry, and can 
be moved forward by screws. 7g. 32 shows this plainly. When the work 
is to proceed each workman takes out one of the foot-plates, a, and removes 
the earth immediately before it to exactly the depth of 6 inches, after which 
he inserts the plate again and presses it firmly against the new wall by 
means of the screws. He then takes up the next plate and proceeds as 
before, until he has pushed forward all its plates, when six inches will 
have been gained on the whole face of the tunnel, and the shield can be 
moved forward by that amount. The newly gained space is immediately 
closed by the arches (jigs. 31 and 32), while the thirty-six workmen in the 
shield proceed to excavate another 6inches. In this manner the pressure of 
the earth is supported at all times, except at the small spaces where the 
earth is just being moved, and these may be closed at once should any 
portion suddenly give way. ‘The form and dimensions of the arches are 
shown in jig. 31. 
The success of the work is wholly due to the use of this shield and 
Brunel’s unflinching perseverance. The shield, which is entirely his 
invention, has been set up by the proprietors of the tunnel as a monument 
in honor of the distinguished engineer. 
589 
