[> 172. ] 
its breadth, in refpedt to the fedtion of the wind: 
the breadth I N being by obliquity reduced to I K. 
The difadvantage of horizontal windmills there- 
fore does not confift in this ; that each fail, when 
directly expofed to the wind, is capable of a lefs 
power, than an oblique one of the fame dimenfions ; 
but that in an horizontal windmill, little more than 
one fail can be acting at once : whereas in the com- 
mon windmill, all the four adt together : and there- 
fore, fuppofing each vane of an horizontal windmill, 
of the fame dimenfions as each vane of the vertical, 
it is manifeft the power of a vertical mill with four 
fails, will be four times greater than the power of 
the horizontal one, let its number of vanes be what it 
will : this difadvantage arifes from the nature of the 
thingj but if we conlider the further difadvantage, 
that arifes from the difficulty of getting the fails back 
again againft the wind, &c. we need not wonder if 
this kind of mill is in reality found to have not above 
7 or -ro of the power of the common fort j as has ap- 
peared in fome attempts of this kind. 
In like manner, as little improvement is to be ex- 
pedted from water-mills with oblique vanes : for the 
power of the fame fedtion of a dream of water, is 
not greater when adting upon an oblique vane, than 
when adting upon a diredt one : and any advantage 
that can be made by intercepting a greater fedtion, 
which fometimes may be done in the cafe of an open 
river, will be counterbalanced by the fuperior refift- 
ance, that fuch vanes would meet with by moving at 
right angles to the current : whereas the common 
floats, always move with the w r ater nearly in the fame 
diredtion. 
Here 
