315 
CHAPTER XI. 
OF THE WATER SCREW. 
THERE is a machine, on the principle of the screw, which 
raises water with considerable power, but not so high as 
the wheel. It is contrived as follows. A beam is pro¬ 
cured whose thickness, in inches, is equal to its length in 
feet ; this is rounded. Its ends, circular, are then di¬ 
vided by compasses, on their circumference, into four or 
eight parts, by diameters drawn thereon. These lines 
must be so drawn, that when the beam is placed in an 
horizontal direction, they may respectively and horizon- 
tally correspond with each other. The whole length of 
the beam must be divided into spaces equal to one eighth 
part of the circumference thereof. Thus the circular 
and longitudinal divisions will be equal, and the latter in¬ 
tersecting lines drawn from one end to the other, will be 
marked by points. These lines being accurately drawn, 
a small flexible ruler of willow or withy, smeared with 
liquid pitch, is attached at the first point of intersection, 
and made to pass obliquely through the remaining inter- 
sections of the longitudinal and circular divisions; whence 
progressing and winding through each point of intersec- 
tion it arrives and stops in the same line from which 
it started, receding from the first to the eighth point, to 
which it was at first attached. In this manner, as it pro¬ 
gresses through the eight points of the circumference, so 
it proceeds to the eighth point lengthwise. Thus, also, 
fastening similar rules obliquely through the circum¬