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Machin',

Fig. 4.

a

Ramsden's in the piece P, and may be tightened in any part of half holes F and T, which were kept together by the Reader's Machine. the slit hy the finger-nut f: this piece serves to regu

screw Z. late the number of revolutions of the screw for each “ H represents a screw of untempered steel, baring, Rambes. tread of the treadle R.

a pivot I, which turns in the hole K. At the other Tig. 1.

“T is a brass box containing a spiral string; a strong end of the screw is a hollow centre, which receives the gut is fastened and turned three or four times round the bardened conical point of the steel pin M. When this circumference of this box, the gut then passes several point is sufficiently pressed against the screw, to pre. times round the cylinder S, and from thence down to vent its shaking, the steel pin may be fixed by tightenthe treadle R. Now, when the treadle is pressed down, ing the screws Y. the string pulls the cylinder S round its axis, and the “ N is a cylindric nut, moveable on the screw H; clicks catching hold of the teeth on the ratchet carry which, to prevent any shake, may be tightened by the the screw round with it, till, by the tooth n working in screws 0. This nut is connected with the saddle-piece the spiral groove, the lever J is brought near the wheel P by means of the intermediate universal joint w, d, and the cylinder stopped by the screw-head .z striking through which the arbor of the screw H passes. A front on the top of the lever J; at ihe same time the spring is view of this piece, with the section across the screw arwound up by the other end of the gut passing round the bor, is represented at X. This joint is connected with box T. Now, when the foot is taken off the treadle, the nut by means of two steel slips S, which turn on pins

the spring unbending itself pulls back the cylinder, the between the cheeks T on the nut N. The other ends Fig. 1, clicks leaving the ratchet and screw at rest till the piece of these slips S turn in like manner on pips a. One axis

t strikes on the end of the piece p: the number of revolu- of this joint turns in a hole in the cock b, wliich is tions of the screw at each tread is limited by the num- fixed to the saddle-piece; and the other turns in a hole d, ber of revolutions the cylinder is allowed to turn back made for that purpose in the same piece on which the before the stop strikes on the piece p.

cock b is fixed. By this means, when the screw is turn" When the endless screw was moved round its axis ed round, the saddle-piece will slide uniformly along

with a considerable velocity, it would continue that mo- the triangular bar A. Fig. 1. & 4. tion a little after the cylinder S was stopped: to pre- "K is a small triangular bar of well-tempered steel,

vent this, the angular lever , was made ; that when the which slides in a groove on the saddle-piece P. The
lever J comes near to stop the screw x, it, by a small point of this bar or cutter is formed to the shape of the
chamfer, presses down the piece x of the angular lever; thread intended to be cut on the endless screw. When
this brings the other end of the same lever forwards, the cutter is set to take proper hold of the intended
and stops the endless screw by the steel pin je striking screw, it may be fixed by tightening the screw e, whichi
upon the top of it; the foot of the lever is raised again presses the two pieces of brass G upon it.
by a small spring pressing on the brace v.

“Having measured the circumference of the dividing. Fig. 1, 2,6. “D, two clamps, connected by the piece a, slide one wheel, I found it would require a screw about one thread

on each arm of the frame. L, and may be fixed at plea- in a hundred coarser than the guide-screw H. The sure by the four finger-screws 6, which press against steel wheels on the guide-screw arbor H, and that on the springs to avoid spoiling the arms: the piece q is made steel E, on which the screw was to be cut, were proto turn without shake between two conical pointed screws portioned to each other to produce that effect, by giving f, which are prevented from unturning by tightening the wheel L 198 teeth, and the wheel Q 200. These the finger-nuts N.

wheels communicated with each other by means of the Fig. 6.

“ The piece M is made to turn on the piece q by intermediate wheel R, which also served to give the the conical pointed screws f resting in the hollow cen- tbreads on the two screws the same direction.

•• The saddle-piece P is confined on the bar A by “ As there is frequent occasion to cut divisions on in- means of the pieces g, and may be made to slide with a clined planes, for that purpose the piece y, in which the proper degree of tightness by the screws n." See Di. tracer is fixed, bas a conical axis at each end, which VIDING INSTRUMENTS, SUPPLEMENT. turns in half boles: when the tracer is set to

any

inclina- For Ramsden's equatorial or portable observatory, see tion, it may be fixed there by tightening the steel screws B. Optics, No 89. and AstronoMY, N° 364. See also a Description of the Engine by which the endless screw

long account of an equatorial instrument made by Mr of the Dividing Engine was cut.

Ramsden by the direction of Sir George Shuck burgh in

the Philosophical Transactions for 1793, art. x. p. 67. “ Fig. 9. represents this engine of its full dimensions In this instrument the circle of declinations is four feet seen from one side.

in diameter, and may be observed nearly to a second. · Fig. 8. the upper side of the same as seen from The glass is placed between six pillars, which form the above.

axis of the machine, and turn round by two pivots pla>“ A represents a triangular bar of steel, to which the' ced on two blocks of stone. See also BAROMETER. triangular holes in the pieces B and Care accurately RAMSEY, a town of Huntingdovshire, 68 miles fitted, and may be fixed on any part of the bar by the north of London, and 12 north-east of Huntingdon. screws D.

It is situated as it were in an island, being everywhere " E is a piece of steel whereon the screw is intended encompassed with fens, except on the west, where it is to be cut; which, after being hardened and tempered, separated from the terra firma by a causeway fortwo miles. has its pivots turned

in the form of two frustumg of cones, The neighbouring meers of Ramsey and Whitlesey, as represented in the drawing of the dividing engine which are formed by the river Nyne, abound with fish, (fig. 5.). These pivots were exactly fitted to the especially eel and large pikes. It was once famous for

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