THE METEOPOLITAN MAIN DRAINAGE WORKS. 
65 
plate, a a', with a deep square gash in the lower part, c, its roof 
resting free upon the rounded end of the vertical bearer, d d 1 , 
of the cradle, e e', which again is supported on two evenly 
turned rollers, //', which have free motion to and fro on the 
flat iron plane, p p r , affixed firmly and truly level on the 
masonry of the pier, m m 1 . These rollers do not rest on their 
axles, but have arches, i i r , accurately turned for the whole 
length of their peripheries, so that 
the axles, g g 1 , turn quite free in their 
sockets, w w 1 . Any danger of lock- 
ing is thus removed, for of course if 
any jambing did take place, it would 
be equivalent to making the culvert 
i a fixture, and damage to the works 
must equally arise when the drain- 
! tube expanded or contracted as if 
the works had been constructed 
without any provision at all. This 
consideration at once explains the 
need for such exceedingly great 
care, in what to the uninitiated in engineering mysteries 
might seem an unnecessary fuss about a trifling matter. 
As barges and vessels pass under this culvert-bridge, 
its lower portion is completely ceiled over with plate- 
iron to prevent damage from the striking of masts or 
spars. The main brick sewers are throughout this district 
carried on a concrete bedding along an embankment ; and are 
also covered over with concrete. At every 
220 yards are man-holes for access to 
the interior, and at every intermediate 110 
yards are air-gratings for ventilation. The 
form of the sewers here is like that of the 
Thames Tunnel, but smaller in dimen- 
sions ; the arch being struck from a 4-feet 
6-inch centre ; the sides and floor being Fig. 7. section of sewer 
portions of circles struck from a 9 -feet giSford ° ld F ° rd and 
centre. 
Three other gaps and watercourses are bridged over 
between the Lea River and the Stratford Road, the prin- 
cipal one being that across the Pudding Mill Stream, the iron 
culverts over which are 252 feet long, and supported on five sets 
of piers. The junctions of the tubes with the brick drains in 
these cases are made with compressed india-rubber inserted as 
a padding at the end of the culvert. 
As the sewage flows from the Stratford Road for the rest of 
the distance to Barking Creek by simple gravitation into a 
large reservoir or receptacle there, and is thence by gates or 
VOL. III. — NO. IX. E 
