[ 25 3 ] 
fig. i. In the lower of thefe bars wx is fixed a 
perpendicular pin, at 3, whofe upper end pafl'es 
through the groove of the bar 4, 5, and its lower 
end through that of the bar N O, and in the upper 
of thefe bars yz, is fixed a perpendicular pin 6, 7 , 
the upper end of which may be taken out, and a 
pencil put in its place ; this pin reprefents the point 
s , and the former pin 3, the point r, in fig. 1. 
There is alfo a perpendicular pin fcrevved to the 
bar 4, 5, at 8, which muff be fixed upon that bar 
diredtly over the groove in the bar FQ^ This pin 
denotes the point a in fig. 1. There are alfo two 
bars 9, 10, and 1 1, 12, with triangular teeth, which 
bars fide in fupporters fcrewed to the frame at proper 
places (which appear at 13, 14, 15, and 16), and 
ride upon the wheels 17 and 18, with fimilar teeth, 
and both fixed on - the axis 19, 20. Thefe wheels 
prevent the faid bars from moving with unequal 
paces, and therefore caufe the bar 4, 5, w'hich is 
fcrewed down to them at each end of it, to move 
parallel to itfelf ; this bar reprefents la in fig. 1. 
Then the aforefaid nuts or Aiders e y f, c, N, and R, 
being fcrewed down at proper places according to 
the coefficients of the equation (as fhall be directed 
more particularly in the next article), and the bar g h 
being pufhed forwards or backwards by the hand, 
will put the whole in motion ; and the pin 6, 7,. 
will defcribe a curve, which fhall be the locus of the 
equation, and the distances where it fhall pafs under 
the filken cord ef reckoning from the pricked line 
upon the bar U X, fhall denote its real roots ; and as 
many times as that pin fhall approach the faid cord, 
and 
