[ 10 ] 
Through the Centre of the Quadrant runs an iron 
Pin , upon which are faftened two fmall round Pieces 
of Wood, which ferve as moveable Radii to defcribe 
the Degrees upon the Quadrant, and as Handles to a 
Velum or Sail, whofe Pianeis one Foot fquare, made 
of Canvas ftretched upon four Battens, and painted. 
On the upper Batten, next to the fhod Rim of the 
Quadrant, is a fmall Spring, which catches at every 
Notch correfponding to each Degree, as the Wind 
fhall, by preffing againft the Sail , raife it up ; and 
prevents the falling back of the Sail, upon the lef- 
fening of the Force of the Wind. At the Bottom 
of the wooden Tube is an iron Index, which moves 
round a circular Piece of Wood faftened to the Top 
of the Pillar on the Pedeftal, on which are defcribed 
the thirty-two Points of the Compafs. 
The Figure of this Machine may be feen Tab. I. 
Fig . 3. Its Ufes are the following : 
1. Having a circular Motion round the iron Axis 
and being furniftfd with a Vane at Top, and Index 
at the Bottom, when once you have fixed the arti- 
ficial Cardinal Points, defcribed on the round Piece 
of Wood on the Pillar , to the fame Quarters of the 
Heavens, it gives a faithful Account of that Quarter 
from which the Wind blows. 
2. By having a Velum or Sail elevated by the Wind 
along the Arch of the Quadrant, to an Height pro- 
portionable to the Power of the Column of Wind 
prefiing againft it, the relative Force of the Wind, 
and its comparative Power , at any two Times of 
Examination, may accurately be taken. 
3. By having a Spring fitted to the Notches of the 
Iron with which the Quadrant is fhod, the Velum is 
pre- 
