MEANS OF COMMUNICATION. 5) 
An improved construction has been sometimes used, which is shown in 
pl. 1, jigs. 16-20. Here we have first a substructure, which of itself is 
a wooden pavement, through which, however, the moisture that penetrates 
from above is drained off into the bed of sand below. /%g. 16 shows this 
substructure, which can be conveniently taken up when water or gas pipes, 
&e., are to be laid. Two or more sills are placed lengthwise at suitable 
distances from each other and united at intervals by cross-ties. On these 
sills rest short pieces of plank, aaa, bevelled at both ends in opposite direc- 
tions (jig. 17), the piece d remaining, however, which prevents the pieces 
of plank from being pushed closely together, thus leaving the interstices ¢¢u 
( fig. 16), which serve as drains. Those pieces which abut against the curL 
of the pavement (jig. 16, left side) are fastened to the sill. No further 
fastening is required, as any pressure acting on the substructure will only 
serve to bring its several parts more closely together. ‘he prisms for the 
_ pavement itself are made of various forms, some of which are represented 
in jigs. 18,19, 20, and 21. Of these jigs. 18 and 19 show a pavement whicis 
is very suitable where the ascent is considerable and the horses require 
a very secure footing. The perspective view (jig. 19) shows the form of 
the single blocks as well as the manner in which they are alternately sc 
placed as to afford a firm step both in ascending and descending. /%g. 2% 
shows a combination of blocks which also forms a very firm pavement. 
They are truncated pyramids, alternately inverted, and two such courses 
will support themselves entirely. 
Great attention is at all times to be bestowed on the cleanliness of streets. 
and especially of wooden pavements, but the cleaning when done by human 
labor is too expensive and slow. Many attempts have been made in 
England and France to perform this labor by machines, and one of the 
most effective of these is represented in jig. 27. It is a street-cleaning 
machine made by Whitworth & Co. of Manchester, where as well as in 
London it has for some time been successfully in use. Two horses with 
a driver can work with a machine of the dimensions given below with 
a speed of 100 feet per minute, and thus can sweep thoroughly in one hour 
120 yards of a street 50 feet in width. 
The machine consists of a cart provided with an apparatus which sweeps 
the street, and carries the dust and rubbish into the interior of the cart. 
when it is moved. In this consists its superiority over other machines of 
this kind, which only move the dirt aside, and leave it to be carted away 
separately. It operates equally well on all kinds of pavements and roads. 
The machine represented in jig. 27 consists of a two-horse cart, a, of ordi- 
nary size, with two large wheels, B ; the body of the cart hangs low between 
the wheels, and consists of two parts, the lower one of which can be taken 
off when full and exchanged for another. or this purpose it is suspended 
by chains passing over pulleys, x. Both pulleys are on the same axle, 
which also carries a cog-wheel that is moved by an endless screw, which 
may be turned by a crank or key in a place accessible to the driver. In 
this way the lower part or box which, when in use, is fastened by bolts, 
may be exchanged for another when required, and thus when the place of 
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