[32] 
38 
the upper surface, or to 6,225,464 square yards, (half of 12,452,928 
squai-e yards) it will amount to 99,6^3,424 cubic yards, or, in round 
terms, 100,000.000 cubic yards. 
As to tlic time neccssai-y to fill them, from observations taken with 
care, from 1817 to 1824, (inclusively) by Mi'. Lewis Brantz, in the 
vicinity of BaltimoFG, Md. we have the followinej results: — In the 
course of eight years, from 1817 to 1824, there fell, on a mean aver- 
age, yearly 39-//o inches. In 1822 there fell the smallest quantity, 
the summer was very dry, vegetation deficient, the crojys of grain 
were short. The quantity of rain which fell tliat year was 29.20 inches. 
The greatest quantity which fell was in 1817, it amounted to J 8.55 
inches. Applying these data to the country round the summit level, 
and using only tlie results of the year 1822, the rain which fell in the 
thi-ee lust and three last months of this year amounted to 16.70 inches, 
whilst that which fell in the same months of the year 1817 amounted 
to 18.40 inches. These 16.70 inches are equivalent to 0.465 cubic yds. 
Thus, during the three first and last months of each year*, there will 
fall at legist 0.46 cubic yards of lain on each square yard of the heads 
of the Youghiogeny, and an area of 217,391,304 square yards would 
be required to collect water for filling the 100,000,000 cubic yards of 
the reservoii's. I'his area amounts to 70-jYo- square miles; and the 
area of the valleys of the two Youghiogenies, above their' Junction, 
and the surface of the reservoirs amounts to much moi-e. Besides, the 
lieads of Cheat river could, jjerliaps, be brought to feed the i-eservoirs. 
These reservoirs once lined, the mass of waltrs which lies lower than 
the head of the feeders, will never alter, and the upj)er part, which 
ft-eds the summit level; will alone require to be lenewed evei-y year. 
We have seen tliat it contains 23,689,007 cubic yardso 
The least quantity of water wliich the gr-eat Youghiogeny gave in 
1824, under the br-idge on the roa<l from Manfield to Moi'ganst(»wn, 
was, on the 21st September, 22.r>8feet in a second. The little YoU' 
ghiogeny gave, on tlie 20th September', 1824, at German br-idge, 4.30 
feet. Total given by tiiosc two streams, in a second, at their lowest 
stage, 26.88 lc*-t. 
This is the minimum which they can give to suj)ply the reservoirs. 
In one month it would amount to 2,580,480 cubic yar'«is; and, suppos- 
ing what is most unlikely, that the two Yougiiiogenies and their tri- 
butaries should remain in this state, and give no more for six months, 
from May to October, it would supply the reservoir's with 1 5,482,880 
cubic yards; and, as during the six preceding months, they would hav(5 
received much more, they would be full at the opening of navigation, 
and receive ever-y month at least 2,580,480 cubic yards as regular 
tribute. 
We d«) not cousidei' in this calculation tJic loss by filtration and 
cvapoi'ation; for-, liy raisijig tlie dams of the reser-voii-s, a quantity of 
water would be added to theui. which would overbalance it. 
^^ e must now conipase iiiose sujjpiies, tlie nunimiiui ol" what tlie 
heiuls (»{ the two Youghiogenies can fuiMiish, wilh the m;L\imum of 
what cither of the t\\ o sumuut le\els will rccuiie. 
