Common 
Graduation. 
=yoew 
The spring- 
dividers. 
PLATE 
CCLXXVIII 
Fig. 5. 
Exemplifi- 
cation of 
their use in , 
the division 
of common 
thermome- 
ters, 
Division of 
sectors and 
plane scales. 
‘ outer edge by a saw. 
352 
of place, and consequent alteration of: the distance be- 
tween the points, prevented. The legs are bored) in 
the direction of their length, to a depth of about 
three quarters of an inch ; they have each, near their 
extremities, a part which projects outwards. These 
parts, as well as the length bored, are cut open on the 
A screw, in each of the project- 
ing parts, passes freely through one-half, but acting in 
the other, brings the parts nearer together, and fur- 
nishes the means of securing the points firmly in their 
places. The points themselves are cylinders, exactly 
filling the bore of the legs, and their ends are worked 
to the requisite sharpness ; and, in order that they may 
measure the shortest possible distance, are brought very 
near the inner, extremity of the diameter. At the very 
point, however, they should be round, and in every di- 
rection the sides must make equal angles with the per- 
pendicular ; for, were they not so, a distance set off with 
them, it is obvious, would be altered by pressure. 
In using this instrument, the fore-finger is pressed 
upon the bow, the thumb and middle-finger keeping 
it upright while the other fingers prop the hand; but 
where a distance is to be set off many times in succes- 
sion, the dividers are to be twirled round in the same 
direction, making a dot at.every half turn. ‘This is 
the manner of handling the tool for common purposes ; 
but for the accurate, bisection of a distance, they must 
not, be touched by any other part than the leg near the 
point, which is lodged. in one extremity, while with 
the other a faint arc is described: the same thing being 
done from the other end of the distance, the middle 
point is secured by making a dot with a fine conical 
pointril. In every use, of the dividers, a magnifying 
glass is to be held in the left hand. 
In dividing a common thermometer, several, points, 
12 or 15 degrees a part, are marked off, according with 
a standard one; these, always unequal, are filled up 
with equal parts, The use of the dividers cannot be 
better exemplified than in this case :, Say the distance 
from one mark to the next is 15°, the operater knows the 
value of his time better than to do this at two operations; 
instead of first dividing the space into. three or five, he 
guesses or estimates the distance of 1°, and running 
the tool over the space almost.as quick as he can count 
its steps, sees how much he has erred; a second or 
third trial never fails to give him the proper distance. 
The dots in these trials, two of which should never be 
made in the same line, are barely to be: seem by the 
glass, and he wants the last, that, by repeating the 
steps with a greater pressure, he may make the dots 
sufficiently large to receive the point of the dividing- 
knife, It may be mentioned, that the operator does 
not draw a line in the direction of his work: without 
such help, he learns by practice to plant his points in 
the direct course, 
Sector and plane scale patterns are divided from a 
diagonal scale, with the square and dividing-knife : 
the whole length of the scale is equal to the radius of 
the sector, and is divided into 1000 parts, and a lower 
subdivision is obtained by estimation. The value of 
each division. is picked. up among the diagonals, ac- 
cording to tables of natural or logarithmic sines, tan- 
gents, &c. Whoever wishes.for full information upon 
this subject, may. consult the Select Mechanical Exer- 
cises of, the late celebrated James Ferguson; every 
table is there given, and not.a figure more or less than 
what is required... The practical part of what is here 
referred to, Mr Ferguson learned. from the first of the 
three Troughtons, to whom his. youngest son James 
Was, apprentice, a youth of considerable promise, who 
died. at, the early age-of; 23 years, 
GRADUATION. 
If it should be thought that wé’ have been unnéces- | 
sarily diffuse in this department of the art,’ we would © 
observe, that should any ‘one, before he is’ fully ac- 
quainted with it, and habituated to the use ofthe tools, 
attempt to practise the higher branches;*he will most 
probably find himself unqualified for the task. = 
"Seer. Il. Engine Graduation... . 
Tue late Mr Henry Hindley of York, ‘about the En 
year 1740, was the first who constructed an engirie for @ 
graduating instruments, and which also served the pur- Hindl 
pose of cutting the teeth in clock wheels. We have it div 
not in our power to give a /particular account of this sim 
engine, but the late Mr Smeaton, in the Phil. Trans. 
for 1785, informs us that the plate was turned round 
by an endless screw, which having been cut with a tool 
that turned upon a centre at a distance equal'to the ra+ 
dius of the plate, made it ‘of smaller ‘diameter inrthe 
middle, so that the screw throughout its whole length, 
acted in contact with the convex edge of the plate. 
Smeaton informs us, that both the screw and the teeth 
in the plate, were uced from’ the original gradua« 
tion of the plate. Keniutenres paper heneralli ied by 
is replete with general information upon thé graduation 
of instruments ; but Hindley’s method of original di- 
viding, and his own improvements thereon, ' form the 
main subject. These will be briefly noticed in the next _ 
Section. sa a : ’ ae 
Hindley, far removed from the metropolis, and: 
haps iccloweig little how, in his time, the Coctdl as 
were cultivated there, was, by dint’ of his own native _ 
powers, making considerable’ ress in. the i . 
ment of his double profession of clock»and instrument 
making. In the latter, however, he must have want- __ 
ed that constant.employment which alone ere 
experience, and give full effect to execution: He 
in the year 1771, at the age of 70-years. ” “mn: » 
An account of the next attempt to make a dividing ye: 
engine was published: at Paris;in 1768, by the Duke de de 
Chaulnes ; every part of which is described with the nes’ « 
utmost minuteness, and illustrated by: 15 folio plates, ™& 
| 
all full of figures. It will mot, however, be*to’ our * 
purpose to give even an abstract of this ingenious work, 
on account of its having been superseded by better con« 
trivances,a due attention to which will occupy asmany 
of our as can) be appropriated: to this subj 
We may however observe, that the wheel of this en« 
gine is not turned round by an endless ‘screw ; itself, 
together with the work to be graduated, is acted:on by 
a clamp and screw for slow motion ; by the latter, a 
divison of the limb is brought to be bisected by the 
vertical wire of a fixed microscope, and then the cor- 
responding division upon the work cut with a point 
pen ara adapted tothe purpose. We do not know 
that any small instruments were ever divided by the — 
Duke de Chaulnes’ engine, or that = large ones. were 
done according to the original method by which it was 
graduated. The method, _—_ interesting, and at 
that time altogether new, will ‘find :the notice it de- 
serves:in that Section of our present article to which it 
belongs. : oon ; 
It is, however, to the ingenuity of the late Mr Ram! 
Ramsden, that the world is indebted for engine divid- ‘ivi 
ing in its full effect. That artist, about the year 1766, 8i®! 
produced an engine which, although it fell far short of 
his expectations, exceeded, in accuracy, the best divid- 
ing plate. It was fully competent to the division of com- 
mon instruments for surveying of land, &c. but was 
deemed insufficient to produce that accuracy whiclris re- 
uired for the purpose of finding the longitude at sea. 
his engine, about 30 inches in diameter, after Rams- 
