PROCEEDINGS OF THE SECTIONS, 341 
When both the works referred to are completed, Sydney may 
boast of a system of sewers that will compare favourably with any: 
modern city as far trunk main sewers are concerned ; but in order 
to secure the full sanitary benefit of such works, two things must 
be attained, viz., that the houses connected with the sewers, before 
any strict supervision was exercised by the city authorities, should. 
be examined for defects in their house-drains and fittings ; ‘ 
secondly, that the sewers themselves should be provided with the 
means of escape for the gases that are continually being given off 
from their contents. 
VENTILATION OF SEWERS. 
It is proposed to deal with the question of the ventilation of 
the sewer first by giving a short description of a few of the most 
favoured . ee by sanitarians in the past and such as 
are in = 
The t that eau itself is the obelisk form of ventilator, of 
which ton in Elizabeth-street, at its intersection with Bathurst- 
street, is an excellent example. 
This obelisk is merely a kind of chimney-shaft, into whieh: is 
connected a branch from “— of several sewers whose nighea 
terminal point is adjacent to 
It was conceived that this ee of shaft ial afford relief to: 
the pressure of gas in all sewers communicating with it, by allow- 
ing such gas to escape through it into the air at its summit after 
passing thr ough several perforated trays of charcoal at its base, 
placed there to absorb the offensive properties of the gas in ques- 
tion. 
This system was in favour among engineers for a long time, 
until systematic experiments were made as to its effect in reliev- 
ter distance than about 300 feet. 
ora therefore, 300 feet be the limit beyond which the uses of 
shafts as ventilators would be reduced to nil, it follows that. this 
would be the greatest distance apart at which such shafts could be 
spaced for the efficient ventilation of a line of sewers; and as their: 
eost each would probably amount to £300 at least, their mere costs 
along with that of the land on which to build them, would re: de 
their use prohibitive. “4 
le obj oe then the appear 
If the cost were not an insuperable obj eee fee 
