[ 2.52 ] 
on the perpendicular pillars EF, GH, IK and L M, 
are fixed three bars ST, U X and Y Z ; on the fir (F 
of thefe S T, is a Aiding nut c, which carries one ex- 
tremity of the bar ab turning upon it as a center ; 
on the fecond and third, viz. UX and Y Z, are nlfo 
two nuts e and j\ which may be fcrew'ed on any 
part of them, and on which the filken cord ef 
is faftned. The two firft of thofe bars, viz. S T 
and U X together with the bar A, or rather lines 
fuch as the pricked line upon the upper one drawn 
upon them from pillar to pillar, reprefent the line 
SS in fig. i. and the filken cord extended from 
the nut e to f and fixed to them, reprefents the 
bafe line Z Z in that figure. 
Then betides thefe there is another rectangular 
figure gbiky about twice the length of the former, 
whofe fides, g k and hi Aide in grooves or fupporters 
fcrewed to the frame ABCD, at proper places (three 
of which may be feen at /, m y and n ), and have 
triangular teeth on their under fides from g to d, and 
from h to <?, which run in fimilar teeth in two wheels 
s and t , of equal diameters, fixed on an axis pqr , 
and their axis pr is fupported by proper cocks, one 
of which appears at Uy the other not feen in this view 
of the figure. Thefe wheels being both fixed to 
the fame axis, and the triangular teeth in the bars 
fitting thofe in the wheels exadtly, occafion the bars 
gk and hi to move with equal paces, when the 
machine is put in motion ; by which means the bars 
vox and yz y which Aide in two pieces i and 2 
fcrewed to the faid bars g k and hiy necefiarily move 
parallel to themfelves : thefe bars reprefent MM in 
