82 ROCHESTER ACADEMY OF SCIENCE. [June 23, 
The foregoing answers one part of the question, and the answer to 
the balance will be found in determining how long a period of time 
would elapse after such bacilli passed into the creek at Springwater 
village before they could arrive at and be distribued through the mains 
in the city of Rochester.. 
The fall of the creek from Springwater village to the head of Hem- 
lock lake is about 60 feet in a distance of a little over three miles by 
the creek, or say 16,000 lineal feet. Assuming a mean velocity of flow 
of one foot per second, the time required for water to flow from Spring- 
water village to the head of Hemlock lake will be 16,000 seconds, or 
say 4.5 hours. The record kept at foot of Hemlock lake shows that 
southerly winds prevailed on 2t days in October, 889, and on several 
of these days the record reads strong south winds, probably 20 to 4o 
miles per hour. In November southerly winds prevailed on 17 days, 
several of these also standing in the record as strong south winds. It is 
known as the result of ten years of observation at the foot of Hemlock 
lake, that, when strong south winds do actually prevail, the water is 
rapidly piled from the south end of the lake to the north end, and it is 
not unreasonable to assume the velocity of the surface of the lake at 
one mile per hour, in which case 6.5 hours would suffice for the passage 
of the germs the whole length of Hemlock lake. 
This assumed velocity of one mile per hour, it may be said, is 
probably considered less than actually takes place at the surface, but as 
a statement of the mean velocity of the water for a few feet below the 
surface, due to wave translation, it fully answers the purpose of a 
general discussion, which is all that 1s required at this time. 
The present compound conduit between Hemlock lake and Rush 
reservoir is composed of about 50,800 lineal feet of pipe 36 in. in diame- 
ter, and 51,500 lineal feet of pipe 24 in. in diameter. The main from 
Rush reservoir to Mt. Hope reservoir is also 24 in. in diameter and 
46,000 feet in length. During the period of time under discussion the 
conduit was acting direct from Hemlock lake to Mt. Hope reservoir, 
and discharging at rate of about 9,000,000 gallons in twenty-four hours; 
or the velocity of flow in 36 in. main can be taken at two lineal feet per 
second, and in the 24 in. main at four and one-half feet per second. 
Making the necessary numerical computation from the foregoing data, 
we find that the time required for passage of water from Hemlock lake 
to Mt. Hope reservoir is thirteen hours, or the total time from Spring- 
water village to Mt. Hope reservoir may possibly be as short as twenty- 
four hours. With an allowance for delay in Mt. Hope reservoir we 
arrive at the conclusion that disease germs, passing into the inlet creek 
