they have written upon the subject, their different modes 
» of ice shall be given in their own words. 
_ Of those numerous capt yaa ay manor 
_. ingenui Rammeeiiin nor have ‘ound useful in 
their oo we say nothing ; for it would be idle to 
obstruct their natural passage to oblivion. 
For the sake of perspicnity, we shall divide this arti- 
cle into three Sections, containing, 1. Common gradua- 
tion, 2. Engine graduation, and 3, Original graduation. 
Secr. I. Common Graduation. 
In this Section of our article will be shewn the me- 
thod of taking copies from a pattern, which has already 
been laid down originally ; or, as indeed is now gene- 
rally practised, taking copies from a copy. This part 
... also includes original dividing, in cases where the usual 
_. patterns do not apply, and where the utmost degree of 
accuracy is not required. 
It will here be necessary to describe the apparatus or 
tools used by the person who divides in common. And 
first the dividing-plate must be noticed. Its dimension 
_. varies-from 14 to 30 inches in diameter. It is either an 
_ entire plate, or a broad rim, connected with the centre 
by four or more radii, and rendered inflexible by circu- 
lar rings, or edge bars underneath. The extreme bor- 
_ der is divided into degrees and quarters ; and just with- 
inthis another circle, into degrees and third parts. 
"Within are usually put such numbers as are required 
__ for the dial of the perambulator ; Gunter’s line of num- 
"bers arranged in a circle, and other logarithmic lines, 
are sometimes inserted. There are also often to be found 
tangents in hundredth parts of the radius, and the dif- 
ference of the hypothenuse and base, as applied to the 
theodolite; also the equation of time for ing ; the 
points of the compass, &c, 
There is always in the centre of the plate a circular 
hole, which should be truly perpendicular to the sur- 
face. Into this. is nicely fitted a pin or arbor, which 
also fits the centre hole in the circle or arc to be divi- 
ded; and while the operation is carried on, is the 
principal. connexion, between them. Fig. 1. Plate 
CCLXXVIII. shews the dividing plate, and its con- 
»XXVIII nection with a compass ring; also a pair of holdfasts 
i for keeping the work from turning round. One of 
| ; these fastenings would be sufficient, were it not neces- 
sary to remove one of them, when its position obstructs 
; the work. An index of tempered steel, usually made 
; of a saw blade, has one of its edges made very straight > 
_-___ At one end a plate of brass, as at A, is rivetted fast to 
( this index, having at its extremity a right angular notch, 
{ aaaahing « little beyond the blade: the angular point 
{ should be exactly in a line with the edge of the index. 
This notch receiving the arbor of the plate, will always 
j direct its edge to the centre. The length of the index 
should be equal to the radius of the plate. To the ex- 
terior end, and below it, is fixed a index B,. 
reaching as far inwards as the original lines of the plate 
extend, which also must have its edge directed to the 
} centre ; but it need not be exactly in the line of the. 
other, and will be better seen if it is placed a little to. 
the right. The figure shews this, and also an arrange- 
ment of nuts and screws, by which the distance of the 
t two parts is to be adjusted, according to the thickness 
t of the work, so that the secondary one may be flat upon. 
{ the plate. The generality of dividers, instead of this 
| contrivance, the index to-suit the different planes 
of the work and ; but this is a very bungling me- 
f thod ; indeed, when the borders of instruments are re- 
} quired to be divided on feather edges, as is the case with 
protractors, bending is necessary :. a very. flexible index 
4 
| 
GRADUATION. 
inclining plane. 
might be employed to advantage, having its position 
adjustable to the plane which is to,receive the divisions, 
The dividing-knife must next be described. This The divid- 
mg 
little implement is represented, in full size, by Fig. 2. 
It consists of a blade and handle ; the former should be 
made of the very best steel, and the latter of beech 
wood. The cutting edge should be exactly of the same 
thickness that the divisions are intended to be ; it should 
be quite straight, and in a line with the handle. This 
edge rust not be sharp like that of a common knife, but 
rounding, so as to present to the surface to be divided 
asmall semicircle, whose radius is equal to half the 
breadth of the line it is to make. At the back the 
blade should be about a fifteenth of an inch in thickness, 
The left “ais which is a wae and downwards in the 
figure, should be und flat; but the o ite side 
must be PB ae ig faint curve from Robes to edge. 
The extreme end of the blade makes with the line of 
the e, an angle of about 70°. A small chamfer on 
the side to the right, broad at the back, but vanishing 
at the edge, reduces the end to an equal thickness. A 
semicircular recess is made in the edge of the blade, 
near the handle, which affords a relief when the tool is 
sharpened, and is farther useful by receiving the inner 
side of the end of the middle finger. For the accom- 
modation of this finger also, a part of the ferrule of the- 
handle is cut away, as represented in the Figure. There 
is a convenience in the back of the blade being formed 
into a curve so as to make it narrow at the point, for 
without diminishing its strength, it enables the operator 
to see his work better. Suchvis the form of the dividing 
knife, an important tool in every branch of the art, as 
in the hands of the best workmen it has continued un< 
altered since the time of Bird. Had we, indeed, been 
inclined to describe it as found in the workshop of an 
ordinary divider of the present time, we should only 
have had occasion to say, that it exactly resembles the 
butcher's cleaver ; and, perhaps, we might add, is com- 
monly directed with about equal science. 
The action of the dividing knife: is directly the re- Mode of 
wes 3 the latter being pushed outwards, using the 
verse of the 
cuts away a fibre in the line of its course, leaving the 
rest of the surface of the metal undisturbed ; but the 
former is drawn inwards, and without producing chips, 
loughs a furrow, and the metal displaced rises in a 
ur on each side. The knife is held very much like a 
pen, only the handle must be quite home between the 
349 
should, in such cases be employed, in order that the Commen 
pressure of the hand may bring it in contact with the Graduation. 
But even here a secondary index “~¥~™ 
F 
dividing - 
knife. 
thumb and fore-finger, which. being placed upon the ~ 
ferrule, directly over the back, is, by its pressure, the 
chief agent in giving depth to the divisions, the thumb 
and middle finger acting as supporters, while the other 
two. fingers, as in writing, prop the hand. The knife 
is held at an angle of about 45° with the plane: to be 
divided, and is used with the flat side in contact with 
the index before described. If it has an inclination of 
its. own to deviate either to the right or left, it is not 
in a condition fit to be used ; for in the former case it 
would require too hard a pressure of the hand to keep 
it in contact with the index, and in the latter would un- 
dermine it, and in either case it would make crooked 
lines, It is therefore n totry it in this respect, 
before the commencement of dividing. If, on drawing 
a line without an index, it deviates to the right, then is 
the vertex of the semicircular edge too near that side ; 
but when that vertex is too near the left, the knife will 
deviate the contrary way. The use of the small cham- 
fer before described is to make the two sides of the 
knife exactly similar at the point ; were it not for this 
