120 TRANSACTIONS OF THE [FEB. 18, 
cient circulation and the water will become stagnant; he even 
speaks of strata of water which will remain unchanged. 
Now, we are in the habit of considering a pure mountain lake 
to be one of the very best sources from which to seek a water- 
supply, and no question is raised about lack of circulation. The 
fact is that it is impossible to keep such water still. It is sub- 
ject to the laws of heat, and there is a constant interchange 
going on between the water at the bottom and at the surface. 
Then it is constantly fanned into ripples by the winds, or lashed 
into waves by storms. 
The proposed reservoir will be a genuine lake, about 17 miles 
long and, except at the extreme upper end, very deep in pro- 
portion to its width. 
As to the upper portion, the building of the Muscoot dam 
now in progress will remove the objection which might be urged 
from this source, by preventing the drawing down of this por- 
tion except in case of emergency. 
The Tyrnwy reservoir for the supply of the city of Liverpool, 
by the building of which one or more villages were submerged, 
is a case in point precisely similar to this,—viz.: the occupation 
of an agricultural valley by a reservoir. 
But the engineers have not left the important matter of cir- 
culation to chance. In arranging for the withdrawal of water, 
the several inlets are fixed at such levels that it can be taken 
from near the surface or from any point below; and, if necessary, 
the whole reservoir could be emptied. Also, by a special sys- 
tem of conduits, either of its three sections can be drained with- 
out entirely emptying the other two. 
It is a confession of weakness to argue that because no such 
dam has been built, therefore it should not be. With our 
present knowledge, the question is simply one of expense. Re- 
cent examinations have discovered a little lower down a still 
better site than that originally fixed upon,—one where the 
rock is found to be continuous and nearer the surface. This 
removes one of the doubts which have been expressed respecting 
the foundations of the proposed dam. 
The question of strength is a simple one when compared with 
many other problems in construction; and there are plenty 
