C r 49 ] 
made by an addition of furface upon the fame ra- 
dius. For this purpofe, the fails made ufe of had 
the fame weather as thofe N°. 8. to 13, with an 
addition to the leading fide of each of a triangular 
cloth, whofe height was equal to the height of the 
fail, and whofe bafe was equal to half the breadth : 
of confequence the increafe of furface upon the 
whole was one fourth part, or as 4 : y. Thofe fails, 
by being turned round in their fockets, were tried in 
four different pofitions, fpecified in N°. 14, 15, 16, 
and 17; from whence it appears, that the bed; was 
when every part of the fail made a greater angle by 
2 ° I, with the plane of the motion, than thofe with- 
out the addition, as appears by N°. 15. the product 
being 820 : this exceeds <$39 more than in the ratio 
of 4 : y, or that of the increafe of cloth. Hence 
it appears, that a broader fail requires a greater 
angle ; and that when the Jail is broader at the ex- 
tremity, than near the center , this Jhape is more ad- 
vantageous than that of a parallelogram *. 
Many have imagined, that the more fail, the 
greater the advantage, and have therefore propoled 
to fill up the whole area : and by making each fail 
a fedtor of an ellipfis, according to Monfieur Parint, 
to intercept the whole cylinder of wind, and thereby 
to produce the greated: effedt podible. 
* The figure and proportion of the enlarged fails, which I have 
found beft to anfwer in large, are reprefented in the figure, Plate VI.. 
where the extreme bar is i~3d of the radius (or whip, as it is called 
by the workmen), and is divided by the whip in the proportion 
of 3 to 5. The triangular or leading fail is covered with board 
from the point downwards i*3d of its height, the reft with cloth 
as ufual. The angles of weather in the preceding note are beft 
for the enlarged fails alfo ; for in pra&ice it is found, that the fails 
had better have too little than too much weather. 
We 
