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power of a fail of 30 feet, to one of 7 feet ; that is, 
when working at a mean rate, the 30 feet fail will be 
equal to the power of 18,3 men, or of 3-3- horfes ; 
reckoning 5 men to a horfe : whereas the effeft of 
the common Dutch fails, of the fame length, being 
lefs in the proportion of 820:44,2, will be fcarce 
equal to the power of 1 o men, or of 2 horfes. 
That thefe computations are not merely fpecula- 
tive, but will nearly hold good when applied to 
works in large, I have had an opportunity of verify- 
ing : for in a mill with the enlarged fails of 30 feet, 
applied to the crushing of rape feed, by means of 
two runners upon the edge, for making oil; I ob- 
ferved, that when the fails made 11 turns in a mi- 
nute, in which cafe the velocity of the wind was 
about 13 feet in a fecond, according to article 6th, 
that the runners then made 7 turns in a minute : 
whereas 2 horfes, applied to the fame 2 runners, 
fcarcely worked them at the rate of 3- turns in the 
fame time. Laftly, with regard to the real fuperio- 
rity of the enlarged fails, above the Dutch fails as 
commonly made, it has fufficiently appeared, not 
only in thofe cafes where they have been applied to 
new mills, but where they have been fubfiituted in 
the place of the others. 
VIII. Concerning horizontal windmills and water - 
wheels , with oblique vanes. 
Obfervations upon the effects of common wind- 
mills with oblique vanes, have led many to imagine, 
that could the vanes be brought to receive the direct 
impulfe, like a (hip failing before the wind, it would 
be 
