[ * 5 ° ] 
We have therefore proceeded to inquire, how far 
the effeCt could be increafed by a further enlargement 
of the furface, upon the fame radius of which N°. 
1 8 and 19 are fpecimens. The furfaces indeed were, 
not made planes, and fet at an angle of 3 5 0 , as Parint 
propofed ; becaufe, from N°. 1. we learn, that this 
pofition has nothing to do, when we intend them to 
work to the greatefi advantage. We therefore gave 
them fuch an angle as the preceding experiments in- 
dicated for fuch fort of fails, viz. 1 1° at the ex- 
tremity, and 22 0 for the greateft weather. By N°. 
18 we have the produCt 1099, greater than N°. 15. 
in the ratio of 7 : 9 • but then the augmentation of 
cloth is almoft: 7:12. By N°. 19. we have the pro- 
duct 1167, that is greater than N°. 17. as 7:10; 
but the augmentation of cloth is nearly as 7 : 16; 
confequently had the fame quantity of cloth as in 
N°. 18. been difpofed in a figure fimilar to that of 
N°. 15, inftead of the product 1079, we fhould 
have had the produdt 1386; and in N°. 19, inftead 
of the product 1167, we fhould have had a product 
of i860; as will be further made appear in the 
courfe of the following deductions. Hence it ap- 
pears, that beyond a certain degree, the more th<* 
area is crowded with fail, the lefs effeCt is produced 
in proportion to the furface : and by purfuing the 
experiments ftill further, I found, that tho’ in N°. 
19. the furface of all the fails together were not 
more than y-8ths of the circular area containing 
them, yet a further addition rather diminifhed than 
increafed the effeCL So that when the whole cylinder 
of wind is intercepted, it does not then produce the 
greatejl eff'eft for want of proper interfliccs to efcape. 
It 
