8 TECHNOLOGY. 
constantly filled up, but after some time the whole mass will attain a high 
degree of compactness and durability.’ - ) 
We have mentioned above that after the superstructure of stones is spread 
on the road, it is pressed and smoothed down by a road-roller. Formerly 
huge cylinders of granite were employed for this purpose; the axle, which 
passed through the centre, rested on bearings in a square frame, which was 
drawn by ten or twelve horses. In modern times cylinders of cast iron are 
used, and we will notice two of the various forms which have been given to 
these rollers. 
The road-roller of Schattenmann consists of a hollow cast iron cylinder of 
4 feet diameter and 4 feet width. On each side is fastened by screws a cross 
of cast iron, through the centre of which the axle passes. On the ends of 
the axle rest cast iron bearings which are attached to the under side of the 
frame which carries a box 6 feet long, 5 feet wide, and 2 feet high, capable 
of being loaded with three tons of stone. Attached to the frame are two 
scrapers of plate iron, two brakes which can be pressed against the cylinder 
by screws, and four rings through which levers can be pressed to prevent 
the roller from upsetting on inclined grades or very soft ground. At each 
end of the frame is a pole and below it a runner, in order to be able to 
reverse the motion without turning the roller round. The cast iron cylinder 
with arms and axle weighs about two tons, the frame and box about one ton, 
and, by loading the roller, the weight of the whole may be increased to six 
tons. P1.1, fig. 22, is a side view of this machine, and fig. 23 a part of the 
section of the cylinder with its arms and axle. a is the cylinder, B the 
frame, c the box, p the brakes, = the adjusting screws for the same, F 
the scrapers, ¢ the runners, # the poles, shown in part, 1 the arched floor 
of the box, x the bar supporting the latter. The roller is drawn by six 
or eight horses, and is at first, passed over the road several times without 
additional load, after which the box is gradually loaded to the full extent. 
In one working-day 2,500 sq. yards may be worked in this way; the road 
must be kept moist, however, the whole time. 
The road-roller by Scheefer is loaded within the cylinder. /%g. 24 repre- 
sents a side view of it, fig. 25 a section of the cylinder, and jig. 26 a hori- 
zontal section of the whole machine. The axle rests in bearings on the 
frame EF, to which the pole B is attached. In the interior of the cylinder is 
a hexagonal system of boxes, 2, 7, 4 (fig. 25), which are held by the arms 7/7, 
and the knees d; these boxes or cells are loaded when required with bars 
of lead or iron, through the openings m, ™, which are closed by covers and 
bars, 6,6 (fig. 24). This roller has the advantage that the axle and frame are 
not loaded as much as in the preceding one, the pressure being more imme- 
diately upon the road; the axle may therefore be of less diameter, and less 
force will be required to move the roller. 
C. Tunnels. 
Tunnels are subterranean roads which are excavated through mountains, 
under rivers, or under structures, in order to avoid the obstacles presented 
to their passage on the surface. The ancients appear to have made tunnels 
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