[ *47 ] 
mean angle, I made the fail, at the middle diftance 
between the center and the extremity, to hand at an 
angle of iy° 41' with the plane of the motion; in 
which cafe the velocity of that part of the fail, when 
loaded to a maximum , would be equal to that of 
the wind, or c = a. This being determined, the reft 
were inclined according to the theorem, as follows : 
Angle with Angle of 
the axis. weather. 
Parts of the 
radius from<: 
the center. 
I - 
- c = ja - - 6f 26' - - 26° 34' 
- C ” <3 - - 69 54 - - 20 6 
- c — a - - 74 19--15 41 middle 
- c — 1 -77 20 - - 12 40 
- c— iia - 79 27 - - 10 33 
- c — 2a - - Si o — 9 o extremity. 
The refult hereof was according to N°. y. being 
nearly the fame as the plane fails, in their beft poli- 
tion : but being turned round in their fockets, fo that 
every part of each fail flood at an angle of 3 0 , and 
afterwards of 6°, greater than before, that is, their 
extremities being moved from 9 0 to 1 2 0 and 1 y°, the 
products were advanced to yi8 and 527’ refpedtively. 
Now from the fmall difference between thofe two 
products, we may conclude, that they were nearly in 
their beft pofttion, according to N°. 7. or fome angle 
between that and N°. 6 : but from thefe, as well as 
the plane fails and others, we may alfo conclude, 
that a variation in the angle of a degree or two 
makes very little difference in the effefl, when the 
angle is near upon the beji. 
It is to be obferved, that a fail inclined by the 
preceding rule will expofe a convex furface to the 
wind : whereas the Dutch, and all our modern 
U 2 mill- 
