3 
defended the then existing system — or rather no 
system — adhered to the largest sized sewers with 
flat bottoms and straight sides, and would have 
had straight tops also had not the superincumbent 
earth required an arched form for its support. 
They went so far as to say that no sewer, as dis- 
tinguished from sewage drains, should be built 
of a less size than would allow a man to walk in 
at hi 3 ease, so that the bottom should be cleansed 
when required. They did not see that a form of 
sewer wtiich involved such aid must from that 
fact be defective, and that the necessity for the 
cleansing and for the dimensions, sprang from 
some error in the design. The propounders of 
small pipes went to the opposite extreme, asser- 
tions being made that an 18-inch pipe would be 
sufficient for the largest branch sewer in Lon- 
don. In this tumult of controversy facts were 
distorted, mis-stated, or ignored, and a vast 
amount of virulent abuse distributed. The 
lapse of time, however, seems to have settled the 
question. Many experiments have been made, 
and sometimes on a very large scale, on the drain- 
age of towns, and it seems conceded that where 
the flow of sewage is considerable, objections 
exist to the employment of stoneware pipes 
beyond the dimension of 1 foot 8 inches by 1 foot, 
the section being egg-shaped. Ordinary street 
sewers can scarcely require a larger section ; but 
when the sewage of a considerable number unites, 
recourse mu3t be had to the brick sewer for 
strength, continuity of bearing, and consequent 
evenness of surface. Beyond the size named it 
is not possible to turn pipe sewers with that 
straightness of line which is essential to the level 
of a sewer and to the perfect junction of the 
connecting ends. It was only after much time 
had been lost and many failures experienced that 
this conclusion was, and then most unwillingly, 
acquiesced in by the advocates of the stoneware 
sewer. 
The form of the sewer, after equal debate with 
that which took place respecting its size, seems 
gradually to have been determined on as much 
from experience as from theory. Whenever the 
section exceeds the general dimensions of 9 
inches by 6 inches, the egg shape is adopted ; 
below that size circular pipes are employed. 
The argument in favour of a circular section over 
a right-lined one is brief and apparently con- 
clusive ; the greatest possible reduction of friction 
is desirable in sewers, and as a curve presents 
within a given length of perimeter less surface 
than a square, so a curved channel— -other 
conditions being equal — must afford less friction 
than a square one. But inasmuch as the 
quantity of sewage is unavoidably to some extent 
variable, and the necessity existing for making 
provision in large sewers for an additional 
quantity arising from the increase of buildings 
would render the channel unnecessarily large 
for current purposes, were the simple circle 
retained, a shape like the section of an egg has 
been devised, which combines the maximum of 
strength, efficiency, and economy. Tlie size 
of such main sewers must manifestly be deter- 
mined by the estimated quantity of sewage they 
are to be constructed to convey, in which the 
future as well as the present must be considered. 
When the egg shape is not available and 
other circular forms are not to be obtained, the 
bottom of the sewer should slope at an angle of 
not less than 45 degrees. The worst form of all 
is a sewer with straight sides and a flat bottom. 
Sewage drains from houses, if of stoneware pipes, 
need never exceed 6 inches in diameter, and 
indeed a 4-inch pipe will generally be found 
sufficient. These are not statements based on 
theory, but are derived from a vast number of 
known and recorded facts. The following rule 
has been given as a good one for the construc- 
tion of sewers : — 
If the diameter of the top arch be 1 
Let the diameter of invert arch be • 5 
And the total depth 1’5 
Then the radius of the arcs which are tan- 
gential to the top arch and the invert 
will also be 1*5 
In other words, the total depth of the sewer 
being six feet, the diameter of the top arch will 
be 4 feet, that of the invert 2 feet, and the 
radius of the side 6 feet. 
The fall of drains and sewers must in some 
measure be regulated by natural slopes ; but a 
rapid incline, followed by one much less steep, 
is conducive to the accumulation of silt at the 
junction. All connections on the same level 
should be circular, and the intersection of pipes 
\%ith sewers should take place at not more than 
half the height of the sewer, the pipe projecting 
slightly, if practicable, beyond its face. A fall 
of not less than an inch in 10 feet is desirable, 
and greater than 2 inches in 5 feet is objection- 
. able, unless tolerable uniformity of slope can be 
secured. In pipe sewers from houses, the fall 
may with advantage be more rapid. 
When the local peculiarities o f ground pre- 
clude a connected or rather continuous system 
of drains, what are termed sumphs are employed 
to carry the sewage from the higher to the 
lower level. They are in fact hermetically closed 
gigantic cesspools, from which the sewage is 
pumped by steam or other power to the Ijigher 
drain, which is to carry it away. Such a plan 
is only to be justified by any other being im- 
practicable. 
tinder almost any circumstances, however, 
sewers will occasionally be subject to obstruc- 
tion from the collection of matters which care- 
lessness or sometimes love of mischief contributes 
to the sewage. Bits of rag, small stones, pieces 
of wood, broken crockery, and other substances, 
are often thrown down the pipes and, lading to 
stop there, are deposited on the invert of the 
main sewer and gradually accumulate a deposit 
around them. The drainage from sinks, 
kitchens, &c., often contains materials of like 
kind. To clear these away, the system of 
flushing lias been employed, although some- 
times its efficacy has been vigorously impeached. 
It simply consists in forcing a large body of 
water, sufficient to ensure a passage of great 
velocity, through the principal sewers, so as to 
