140 J. ASHBURTON THOMPSON. 
thoroughly as possible for reasons attaching to ‘health; and it 
would be foolish not to take advantage of the opportunity which 
sewerage-construction affords to arrange for their thorough drain- 
age. Nevertheless, this also is a matter quite separate from 
sewerage. That point is now pretty generally recognized even 
by engineers of the old English school ; and, asa rule, they admit 
that all sewers should be water-tight. As for us, I hope and 
believe that we here are unanimous in demanding that they shall 
be watertight. This indeed is as important to the success of the 
engineer’s calculations as it is to health, and that is some security — 
that watertightness will be attempted. Subsoil waters, then, 
belong to the category of rainwater ; they are not sewage. Often 
the cuts will do much to relieve the subsoil without any special 
work being put in to ease it. But it is possible, and when neces- 
sary it is proper, to lay a line of drain tiles in the same trench 
with the sewer, which drain tiles may turn aside from the sewer 
line at any convenient point from which an outfall to the natural 
surface can be got, or to an underground drain in case it has been 
necessary to construct one. That, I think, is enough to say of 
subsoil waters. A scheme of sewerage that does not provide for 
carrying them off (and, when necessary, for lowering the ground | 
water too) is imperfect from the sanitary point of view. It does 
not cost much extra to drain them; they are not sewage, and 
therefore should not be admitted to the sewers. 
I do not think I need say more upon the principles of the 
separate system and of the objections raised against it. Of the 
latter I have endeavoured to express my opinion clearly and 
forcibly so that discussion may be the easier. Ido not think 
there is much in them at the most; they are for the most part 
theoretical difficulties which disappear as soon as the experimental 
test is applied to them ; and they certainly do not weigh one grain 
against the system when the question is one of securing sewerage 
at a moderate cost for a country town in Australia. 
Let me, before I sit down, recall to you the characteristics of 
the separate system as regards construction. Moderate size of 
