[ ! 5 ° ] 
vantage in all fixed engines, that are loaded with 
heavy weights ; efpecially when the power that ope- 
rates is expensive, as men, horles, fire, &c. And in 
finer kind of engines, where it may be neceflary 
to avoid any obdrudion from fridion as much as pol- 
fibie, the double, or treble wheels, where there is fuf- 
ficient room, will reduce the quantity to any degree 
that can well be required. 
Another advantage alfo arifes from the application 
of thefe kind of wheels, that, if the motion is requir- 
ed to be extremely fwift, though the pevets be as 
imall as the weight they fuftain can allow of, yet 
they fcarce ever wear the holes they turn in ; for the 
lad pevets in a treble fet of wheels, which are the 
only ones that rub on a dead furface, will hardly 
make one revolution in two days. 
There are feveral engines to which thefe wheels 
might be applied to advantage, even where the aid- 
ing power coifs nothing ; as watermills, where water 
is not always to be had plenty, which, by this means, 
would grind with much lefs water. Windmills, par- 
ticularly, muff receive great benefit from them ; the 
fhaft being fo large, the quantity of fridion, which 
is in proportion to the part rubbing on a dead furface, 
mud be greater in this, than mod other engines ; be- 
fides, the rubbing part being wood, mud did in- 
creafe the quantity: I Ihould therefore imagine, that, 
if the draft were placed on wheels 5, or 6 feet dia- 
meter, it would not require above half the drength 
of wind, necelfary at prefent. The frame in which 
thefe wheels might be placed, could eafily be made 
in luch a manner, as to be lowered, or railed ; fo 
that if any inconvenience were found from too great 
velocity 
