368 On Drainage and Sewerage of Towns. 
the construction of a given length is much less, and 
the strength to resist the tendency of the earth to press 
in the sides of the sewer is far greater, than in one with 
upright sides. 
It is most desirable that the entrance into these branch 
sewers from the street, as gulley-holes, &c., should be 
carefully trapped, so as not to allow the stench from the 
refuse contained in them to make its way into the streets 
or into the houses. 
It is not necessary that I should enter more at length into 
details, my object being to lay before the Society the 
general principles which should guide those who are called 
upon either to submit or discuss plans for a comprehensive 
scheme of drainage for towns, together with such general 
observations upon form and materials as may be useful 
as hints. 
In applying these observations to the towns of this colony, 
but more especially to Hobart Town, I would observe with 
reference to the directions of the main sewers, that the lines 
in which these will run are plainly determined by the outline 
of the land upon which the town is built. The Hobart Town 
Rivulet is the great outlet, not only for the town itself, but 
also for the side of Mount Wellington and the various 
gullies which are formed in the flanks of the mountain. 
In heavy rains, the rush of water from the hills is go 
great as to fill the present watercourse nearly to the brim at 
the lower part, near the outfall into the river. It would 
not, therefore, be practicable to diminish the section of 
the channel here, though at points higher up the stream, 
where the fall is greater, a reduction might of course be 
effected. 
At Launceston, the shape of the ground would also seem 
