C 122 ] 
Observations. 
Obferv. iff On comparing column 2d and 4th, 
Tab. I. it is evident, that the virtual head bears 
no certain proportion to the head of water ; but that 
when the aperture is greater, or the velocity of the 
water ifiuing therefrom lefs, they approach nearer to 
a coincidence : and confequently in the large open- 
ings of mills and fluices, where great quantities of 
water are difcharged from moderate heads, the head 
of water, and virtual head determined from the ve- 
locity, will nearly agree, as experience confirms. 
Obferv. id. Upon comparing the feveral pro- 
portions between the power and effect in column 
1 1 th, the moff general is that of 10 to 3 ; the ex- 
tremes 10 to 3,2 and 10 to 2,8 ; but as it is obferv- 
able, that where the qu'antity of water, or the ve- 
locity thereof 3 that is, where the power is greateft, 
the 2d term of the ratio is greateif alfo : we may 
therefore well allow the proportion fubfifiing in large 
works, as 3 to 1. 
Obferv . The proportions of velocities be- 
ween the water and wheel in column 1 2, are con- 
tained in the limits of 3 to 1 and 2 to i; but as 
the greater velocities approach the limit of 3 to 1, 
and the greater quantity of water approach to that 
of 2 to 1, the befl general proportion will be that 
of 5 to 2. 
Obferv . 4 tb* On comparing the numbers in 
column 13, it appears, that there is no certain ratio 
between the lead that the wheel will carry at its 
maximum , and what will totally flop itj but that 
they are contained within the limits of 20 to ip, and 
3 of 
