42 Transactions.— Miscellaneous. 
In estimating the quantity of sewage to be carried off ** provision has 
been made for an increase of the population up to 80,000 people to the 
square mile, except over the outlying districts, where provision has been 
made for a population giving 20,000 to the square mile." “An improved 
water supply, equal to five cubic feet, or 814 gallons per head for such 
contemplated increased population has moreover been anticipated." 
Again: “How to dispose of the rainfall is a question of considerable 
difficulty, and has given rise to much diversity of opinion. This arises 
from the fact that, whilst it is in itself harmless, and even advantageous to 
the river, it sometimes falls suddenly in large quantities. These considera- 
tions have induced theorists to advocate that the rainfall should not be 
allowed to flow off with the sewage, but should be dealt with by a separate 
system of sewers. This theory however is most impracticable." 
Referring to experiments on this subject the result ‘‘ distinctly establishes 
the fact, that the quantity of rain which flowed off by the sewers was, in all 
cases, much less than the quantity which fell on the ground,” also “that 
1 of an inch of rainfall will not contribute } of an inch to the sewers; 
nor a fall of 4$; of an inch more than } of an inch." 
Again: “ As it would not have been wise or practicable to have increased 
the sizes of the intercepting sewers much beyond their present dimensions 
in order to carry off the rare and excessive thunderstorms, overflow sewers, 
io act as safety valves in times of storms, have been constructed at the 
junctions of the intercepting sewers with the main valley lines.” 
Again: “ Having determined the quantities of sewage and rainfall to be 
carried off, and the rate of declivity of the sewer required for the necessary 
velocity of flow, the sizes of the intercepting sewers were readily determined 
by the formule of Prony, Eytelwein, and Du Buat.” 
Again: “A primary object sought to be attained in this scheme was 
the removing as much of the sewage as praetieable by gravitation, so as to 
reduce the amount of pumping to a minimum." Under this view, on the 
north side of the Thames, the high level sewer commences at the foot of 
Hampstead Hill, passing through certain distriets of London, draining about 
ten square miles (shown in the plan), the form of which **is mostly circular, 
and it varies in size from 4 feet in diameter to 9 feet 6 inches by 12 feet; 
its fall is rapid, ranging at the upper end from 1 in 71 to 1 in 876, and from 
4 feet to 5 feet per mile at the lower end.” 
The middle level sewer is as near the Thames as the contour of the 
ground will allow, the area intercepted being 17} square miles. 
The low level sewer intercepts the sewage from the low level area, which 
contains 11 square miles? ‘It is also the main outlet for a district of about 
