C 159 J 
city of the wind, and ultimately in that ratio pre- 
eifely. Hence alfo we fee that windmills, fuch as 
the different fpecies for raifing water for drainage, 
&c. lofe much of their fulleffed, when ading againft 
one invariable oppofition. 
V. Concerning the effects of fails of different magni- 
tudes , the flrudlure and pofition being ffmilar , and 
the velocity of the wind the fame . 
Maxim 6 . In fails of a fimilar fgure arid pofition, 
the number of turns in a given time will be recipro- 
cally as the radius or length of the fail. 
The extreme bar having the fame inclination to 
the plain of its motion, and to the wind ; its velocity 
at a maximum will always be in a given ratio to the 
velocity of the wind ; and therefore, whatever be the 
radius, the abfolute velocity of the extremity of the 
fail will be the fame : and this will hold good re- 
fpeding any other bar, whofe inclination is the fame, 
at a proportionable diftance from the center ; it there- 
fore follows, that the extremity of all fimilar fails, 
with the fame wind, will have the fame abfolute 
velocity ; and therefore take a fpace of time to per- 
form one revolution in proportion to the radius ; or, 
which is the fame thing, the number of revolutions' 
in the fame given time, will be reciprocally as the 
length of the fail. 
Maxim 7. The load at a maximum that fails of 
a fimilar figure and pofition will overcome , at a given 
diftance from the center of mot ion , will be as the cube 
of the radius. 
Geo* 
