1891-92. | LAKE CURRENTS. 279 
possible how far the current of the river could be traced across the lake. 
We put out a number of floats inside the bar and in the mouth of the 
river, but unfortunately we gave the floats too much line and most of 
them grounded on the bar; one or two that got over safely took an 
easterly direction. There is a distinct color line dividing the water 
inside the bar from that outside, and the difference in temperature is very 
marked. In the river, both at the surface and at the bottom the temper- 
ature was as high as 69° or 70°, while outside, at the depth of 400 feet, 
we found the water at its maximum density or 39°5° Fh. This accounts 
for the coolness of our water supply in Toronto; although it primarily 
comes through the Niagara river and is heated up to the point already 
indicated, before it reaches us it has to come over that cold sub-stratum 
of water, at least for thirty miles; so that at the intake in the month of 
July, we found the temperature as low as 43°; in October it was observed 
to be the same, and only slightly higher in August and September. 
As the practical outcome of these investigations is to ascertain with 
what degree of safety sewage may be deposited in the lake, it becomes 
necessary to consider another factor that enters into the question, viz., 
the effect of diffusion upon sewage. The share of the work, in these in- 
vestigations, carried out under the superintendence of Dr. Mackenzie, on 
behalf of the Provincial Board of Health, will afford material aid in 
solving this problem; the substance of which will be found in the 
following quotation from Mr. Rust’s report. ‘“ To ascertain, if possible, 
from actual tests, how rapidly diffusion and oxidation take place, Mr. 
Mackenzie, on the 16th October, took samples of water, in a direct line 
from the mouth of the intake to the outlet of Garrison Creek sewer, 
which discharges 400,000 cubic feet, per day. I attach a copy of the re- 
sults, by which you will see that the sample taken within a little over half a 
mile of the mouth of the sewer came within the limits of first-class water ; 
the wind on the occasion was from the North, which would tend to carry 
the sewage direct to the intake. This shows very favorable results, and 
tends to prove that there will be no possible danger of contaminating the 
water supply if the sewage be discharged into the lake at a distance of 
six miles east of the intake. When the population of the city exceeds 
500,000, and it is found that there is the slightest danger to the water 
supply, precipitation works could be erected and the sewage treated by 
chemical means.” The copy of the schedule referred to shows that a 
sample of water taken near the mouth of the sewer showed a degree of 
organic impurity by Muter’s scale of 2°44 per million, while first class 
water should not show above ‘25. It also showed as high as 40,000 
bacteria per cubic centimetre; yet we find that within half a mile, this 
water is raised to a standard of first class purity. We can then judge of 
