Construction, Cost, Repair, and Management. 397 
neighbours as in a piece of mosaic work, where no space is left 
for water to penetrate, is thus destroyed, as this effect can only 
be obtained with stones of an angular shape. To prevent this 
damage, the newly-laid stone is often covered with gravel, which 
fills up the interstices, and causes the surface at once to become 
set and firm. If this is followed by rolling, a thoroughly 
smooth and impermeable surface is at once formed. The ap*- 
plication of steam to this purpose, by doing away with the 
objection arising from the displacement of the stones by the 
feet of the horses used in moving the rollers, has placed at the 
disposal of road surveyors the means of repairing roads in a 
thoroughly efficient manner. 
The main objection to the application of gravel, or screened 
granite, lor the purpose just described, is the necessity of sub- 
sequently removing a great portion in the shape of mud ; but 
the interstices must be filled in some way to prevent the lodgment 
of wet, and to fix the stones. It is better to supply this, rather 
than allow it to be supplied by the wearing away of the 
road-material. 
The great essential in the economical maintenance of roads 
is to keep them clean, and free from mud and wet. Nothing 
destroys the surface of a road more than allowing the mud 
arising from the wearing away of the material, and the droppings 
of the horses, to remain on the surface. In winter it acts like a 
wet blanket, preventing the sun and wind from drying the road ; 
and in summer it causes clouds of dust which, blown about by 
the wind, are not only a source of physical discomfort, but have 
a very detrimental effect upon health, by conveying to the lungs 
organic and mineral matter of a highly injurious character. 
On highways repaired with limestone and similar soft ma- 
terial a great deal of cleaning is necessary. For this purpose 
several machines have been invented, by which the work is ac- 
complished at much less cost than by hand-labour. It has been 
estimated by the makers of these machines that the cost of remov- 
ing dirt from roads by hand-labour varies from 20s. to 305. per 
mile, whereas the same man can accomplish the same amount 
of work with a scraping-machine for from As. to 6s. The cost 
of a hand-machine is about 3/. 10s. Horse scraping-machines 
are also made, which are stated to scrape 10,000 superficial yards 
per hour, the horse moving at the rate of three miles an hour_ 
The cost of the machine, which is supplied by Messrs. Smith 
and Son, of Barnard Castle, is 15Z. 
A machine has also been invented by the same firm for 
sweeping roads by horse-power, which, according to the state- 
ment of the makers, is capable of sweeping 15,000 yards in an 
hour. It consists of a circular brush, which revolves by means 
