tly 
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hand, till the biseetion’I was bro 
The: 
im i Ny 
from end to end, with- 
plate from the screw, till the 
The notched endless screw, with the rod and winch, 
were then removed, and the plain screw was put in its 
place; having the divided wheel on one end of the 
screw arbor, and two sets of ratchet wheels on the 
other end. These sets are each d of three 
wheels, having teeth round their circumference ; one 
in each set hath’ $2 teeth, another 48, and’ the third 50, 
These two sets being one for turning the screw, and 
the other for ing it, they have, for this purpose, 
their ratchet cut in opposite directions, 
2, I, represents a cylinder of brass, having on one end 
two steel rings a and 6, with their edges: that are to- 
wards each other cut into ratchet teeth; these teeth are 
eut in contrary directions, so as to fit into each other ; 
on one of these rings is an index, and the other hath its 
teeth numbered with 10, 20, up to 50. The other end 
_ of the cylinder is made hollow, and contains one of the 
sets of ratchet wheels. There are two slits opposite 
each other, pierced through the hollowed part of the 
cylinder W. In each of these slits is a click turning 
on an axis, and is pressed into the teeth of the ratchet 
wheel by a small spring. The clicks may be moved 
along their axis, so as to catch in any one of the three 
ratchet wheels, and may be fastened at that place, by 
tightening the small screw S. 
The cylinder I, with the clicks, &c. turns on a steel 
axis X, attached to the piece K, and in a line with 
the axis of the endless screw. | Motion is given to this 
cylinder round its axis by a piece of cat-gut, which hath 
one end fastened to the ratchet ring 4; and the other 
end, after passing four or five times round the cylinder, 
is fastened to a treadle; and on pressing the treadle 
downwards, the clicks S catch in the teeth of one of the 
ratchet wheels, by which means the cylinder I, toge- 
ther with the endless screw, are turned round their 
axis, which moves: the sn a the iron re and 
_ at the same time winds up the spiral spring w. re- 
leasing the treadle, ‘the spring stttidennde itself, the 
clicks quit the ratchet wheel, and leave the endless 
~ serew at rest, while the cylinder I turns in an opposite 
direction, and raises the treadle to where it was before. 
V is a small square bar of steel, having both its ex- 
tremities cylindric. These cylinders move in holes 
lined with hardened steel, one in the piece D, and the 
other in the piece K. This bar earries three different 
pieces, which are of tempered steel ; the middle one ¢, 
as made to lie in the interval between the threads of the 
screw cut on the cylinder, and passes nearly half round 
its circumference ; it is kept in the threads by a spring 
e, which presses oma piece g, screwed to the iron frame. 
eps : aa to the bar V, by the screw 
turning the cylinder on its axis, will give a longit 
nal motion cs oa bar V. = 
€ upper of the piece f is formed into a hook, 
and may be set to catch in coe of any of the ratch- 
et wheels, and then fastened to the bar v by the screw 
i. Towards the other end of the bar is a piece j, which 
Serves to stop the cylinder in turning back, so as to li- 
2. 
+ ad number of pot amen or . It is fastened 
to i place on bar v, by tlie finger screw f. 
When oe engine is used, the Greeetrarrs. 
GRADUATION. 
359 
wards, which, by means of the cat-gutstring, turns the _ Engine 
linder I round its axis; and the piece ¢ moves along @tduation. 
the thread, till a stud r on the cylinder; striking on the .~ my 
top of the curved piece ¢ bends the spring é, till that Rarmsden’s 
piece rests on the piece g. By bending this eprings the straight line 
square Bar is turned a fivtle on its axis, and pulls the engine. 
hook f into the teeth on the ratchet wheel R. Then 
releasing the treadle, the spiral spring turns back the 
linder, till the: piece 7 is fone under the stop on 
ratchet ring 4. : 
The parts of a revolution are regulated, by setting 
the number required on the ratchet ring 4, to the index pigs, 1, 2 
on the'fixed ring a. Each of the teeth answers to a mo- 
tion’ of +44, of an inch of the plate A; and the num-« 
ber of revolutions, each of Which moves the plate A 
véy inch, is regulated by setting the piece jon the bar. 
resents the steel frame, in which the tracer is Pigs, 1, 2, 
fixed. This frame turns between the conical points of 3: 
two screws n, n of tempered steel, which are screwed in 
the frame Q. There are also two similar screws in the 
same frame at m, m. The;points of these screws, which 
are also of tempered: steel, turn in conical holes in 
the piece P. By means of this parallel motion, the tra- 
cing point, by which the divisions are cut, will always 
describe ‘the same line without any lateral bending. 
The tracer is put in the hole in the axis 4, and is fixed 
there by tightening the four screws /, which presses the 
piece c against the flat part of the axis. 
This axis, which hath its pivots formed in double 
cones, turns between the ‘half holes at d, andmay be 
fixed when the tracer is set to any required inclination, 
by tightening the screw S. : 
S$ is a brass ruler, having its edges very straight and 
parallel. It hath two thin pieces of steel ¢ attached to 
it, which turn on joints at A, exactly equi-distant from 
the edges of the ruler. The interval between the pieces 
> , is exactly the same with the width of the steel 
Fake L. There are angular notches on the lower edge 
of the pieces g; similar and equi-distant from their cen- 
tres; so that when’any two corresponding notches are 
put on the screws n,n, between the frames Q and L, 
the screws being on that part made cylindric, and both 
of the same diameter, then the edge of the ruler will al- 
ways be at right angles to a line drawn by the tracer. 
The ruler S, in this manner attached: to the cutting 
frame, may be set parallel, or to any required inclina+ 
tion with the edge of the plate A, by turning the hans 
dle T, which moves the piece P with the cutting frame 
and ruler on the centre x, and may be fixed thexe by 
tightening the nut P. 
From a centre J, on the plate A, are drawn two cir- 
cular ares. The outer one is divided into degrees, dnd 
numbered from 1 to 9. Each degree is again subdivi- 
ded into six parts, or every ten minutes. The inner 
circle is divided in the proportion, that the cosines of 
the angles of inclination with the edge of the plate A 
bears to the radius, supposing the radius 10,000, and 
the divisions’are numbered ‘every 10th with 10, 20, to 
140, But the use of this apparatus may be perhaps bet- 
ter understood by an example. 
Let it be required to divide a line of the length of 
9 222., into the same number of divisions, and in the 
same: manner as if it were 10 incheslong. Put the ru- 
ler Sto the cutting frame L, and turn the handle T till 
the same edge of the ruler cuts’ the centre J, and the 
first division from the O of the inner arc. ‘Then screw 
the instrument to be divided firmly on the plate A, so 
that the line to be divided may be parallel to the edge 
of the ruler, which may be now removed. When 
plate has moved 10 inches in its own direction, the 
PLATE 
CCLKXXX. 
Figs. 2, 4. 
Fig, 6. 
