[ H5 3 
Obfervations and Deductions from the preceding 
Experiments. 
I. Concerning the bejl Form and Poftion of Wind- 
mill-Sails. 
In Table III. N°. i. is contained the refult of a 
fett of experiments upon fails fet at the angle which 
the celebrated Monf. Parint, and fucceeding geome- 
tricians for many years, held to be the bed ; viz. 
thofe whofe planes make an angle nearly with 
the axis ; the complement whereof, or angle that the 
plane of the fail makes with the plane of their mo- 
tion, will therefore be 35 0 , as fet down in col. 2. and 
3. Now if we multiply their number of turns by 
the weight they lifted, when working to the greated 
advantage, as fet down in Columns j. and 6 . and 
compare this produdt (col. 8.) with the other pro- 
ducts contained in the fame column, indead of being 
the greatelf, it turns out the lead: of all the red. 
But if we fet the angle of the fame planes at fome- 
what lefs than half the former, or at any angle from. 
1 5 0 to 18 0 , as in N°. 3. and 4. that is, from yz° to 
yf with the axis, the product will be increafed in 
the ratio of 3 1 : 47 ; and this is the angle mod com- 
monly made ufe of by pra&itioners, when the fur- 
faces of the fails are planes. 
If nothing more was intended than to determine the 
mod efficacious angle to make a mill acquire motion 
from a date of red, or to prevent it from paffing into 
red from a date of motion, we diall find the pofition 
of N°. 1. the bed ; for if we confult col. 7. which 
contains the lead weights, that would make the fails 
pafs from motion to red, we diall find that of N°. 1. 
V o l. LI. U (relative 
