GRADUATION 357 
just its height; to suit the thickness of the work to be of my own construction, and as it was easy to make Engine 
: 4 them, whether or small, to suit my arbor, by fix- Graduation. 
| ‘Fig. 
ie 
tripdd, a cross piece L, 
2, nearly the length of the screw arbor, and paral- 
lel to it, is firmly fastened. This carries upon its extre- 
mities two pillars similar to, but smaller than, the others. 
‘part can crossing pieces be admitted; for as they form 
ing it, I avoided one source of uncertainty and error. 
This arbor is the principal connection between the en- 
gine and work to be graduated, and requires the most 
exact fitting ; and tapped holes, arranged yariously 
s Upon the strong bar KK, at equal distances from the through the len of the 12 radii, furnish the means 
_ middle, are two other bars fixed by rscrews. They of applying holdfasts, to prevent accidental circular de- 
extend from the ar bar» to the pillars in front, to rangement. 
which they are secured by double nuts like the former. «1 will now conclude this long description with ob- 
‘These two bars,»marked M, M in the plan, are bound serving, that with this engine, and indeed the observa- 
together 2 brace at the remote end, and by tion applies equally well to those of Ramsden’s construc- 
another a little way beyond the centre. But in no other tion, the operator can cut about 24 strokes in a minute 
of time ; for: one single minute indeed, he will be able 
‘the support for apparatus; that cuts the divisions,  to»make 30; but including short and frequent in- 
“uninterr motion along the whole line of the radius tervals of rest, the former rate yw f be kept up for hours 
is requi Wha Leas together. The vast importance of this expedition, needs 
«The rere apparatus consists of three principal “no:comment with those who know the value of accu- 
‘pieces, marked in the:plan a, ¢, 0. The first isa bridge, - rately graduated nautical instruments, and the great 
which crosses the space between the bars M, M, and to Semel or them. Yours, &c. Epwarp Troveuton,” 
which it is attached at either end by sliding sockets. 
_ The latter run along the bars, to any part of which the 
seppeeind may be clamped, according to the length of ating circles and ares; yet we should not think that 
radius of the instrument to be graduated. Two justice was done to our article, were we to omit an ac- 
“steel screws having conical points, are tapped through count of one for the former purpose. 
the perpendicular ends of the bridge above the sockets, Encouraged by his former success, and having in 4 ccount cf 
-and by working in holes of the second piece, form an . prospect farther rewards, of which he was not disap. Ramsden’s 
axis or joint, round which the latter has a freeand steady pointed, Mr Ramsden constructed the first right-line straight line 
motion. The third: piece, the form of which, aswell engine, an account of which was published in 1779, °¢"“ 
as that of the second, is seen in the plan, has, like the 
first, steel screws with conical points tapped through its 
vends, and these like the others act in the middle piece, 
forming another horizontal axis parallel to the former, 
and in every like it. In Fig. 1, the parts are 
extended, for the purpose of being more distinetly re- 
; into a position in which they cannot work. 
The best effect is produced, when the middle piece is 
vertical, and the third horizontal. Sufficient freedom » 
of action, however, is found in this contrivance of Hind- 
ley’s, to produce a rectilinear motion of the pointril of 
at least one-third of an inch, a quantity fully adequate 
to the purposes required. The part of the third piece 
~next the centre, is that in which the pointril is placed. 
“It is so contrived, that its length below the piece may be 
- varied rat per api that it may be turned round upon a 
horizontal axis, so as to make any angle with the plane 
to be divided upon, and that its action may be view 
by a properly attached magnifying-glass, - 
._, There is one part, which might either have been men- 
tioned sooner, or, as the performance of the engine in 
point of accuracy is not at all promoted by its introduc- 
"tion, t have been altogether omitted; but as it 
bears rather a conspicuous appearance in Fig. 2, it may 
as well be noticed. A bar attached to the same pieces 
that support the screw arbor, to which it is parallel, 
and placed below it, together with a cock behind, bear 
the axis of a vertical friction wheel N. This wheel is 
placed so, as to roll in contact with the under side of 
the limb of the engine immediately below the dividing 
“screw. Without this, the action of the screw in the 
teeth of the wheel would occasionally produce a very 
harsh jarring sound, but which is pa er) mute by 
On innivesdand , 
ae len tempered steel arbor rises full two 
inches above the surface of the » inthe axis of 
which _ “2 ae fixed. In other engines the 
axis 1s hollow, into which may be dropped different] 
sized arbors, suitable to the Sa holes of the bred 
ments to be graduated ; but as I never intended with 
this engine to divide any other instruments than those 
We are well aware, that engines for dividing straight 
lines, are of much less importance than those for u- 
~by,-order of the Board of Longitude. Of this, the 
- following is a copy, accompanied by reduced drawings 
of the original ny Se 
« Experience having evinced the great utility of the 
engine for graduating circles, it encouraged me to at~ 
tempt a similar method, -whereby lines of equal parts, 
sines,. tangents, secants, &c. might be divided with 
equal ease and correctness. 
By the engine hereafter described, any line of equal 
parts, &c,,may be divided without an error of the 
acocth part of an inch ; and, as this can be done by 
any indifferent person, and so very expeditiously, its 
uses for dividing all sorts of navigation scales, sectors, 
&c. must be obvious ; especially when it is considered, 
that from the incorrectness of the present method of 
dividing, these valuable instruments are of less use 
than they might be. 
This engine consists of a strong plate of brass, moye- 
able on two edges of an iron frame. To facilitate its 
motion, the friction is considerably diminished by the 
application of three rollers to the under-side of the 
one : the iron frame is, supported on a strong maho- 
gany stand. 
One edge of the brass plate is ratched or cut into 
teeth, of which there are exactly twenty in an inch, 
and it is moved along the iron frame by an endless 
screw, having exactly the same number of threads in 
an inch ; these threads fit into the teeth on the brass 
plate. Each revolution of the endless screw round its 
axis will move the plate -£;th of an inch along the iron 
frame. 
A small wheel is fixed on one end of the screw, hav- 
ing its circumference divided into 50 parts, which are 
again subdivided into five parts by a vernier; there- 
fore, when the screw is turned on its axis, one of the 
primary divisions, the plate will be moved ,-4,th of 
an inch along the iron frame ; if the screw be turned 
to the coincidence of one division on the vernier, the 
plate will be moved 752,,th of an inch, and so-of the 
rest ; and the line on the plate to be divided, which 
terminates the spaces moved by the brass plate, may be 
