A roasting jack to be turned by the descending power of a weight, is shewn in Fig. 3. A is the barrel on which the cord for the weight winds. The barrel is not fixed upon the main axis, which is shewn by dotted lines: It slips round upon it quite freely in the direction proper for wind ing up the i eight; but is prevented from turning in the other direction, by a ratchet concealed within the barrel near the cog wheel B. The cog wheel B is fixed fast on the main arbor, and its teeth turn a pinion b on one end of the arbor C ; the other end of this carries a worm wheel, which cannot be seen in the drawing, but its teeth act in the worm cut on the vertical spindle T. On the top of the spindle is the flywheel 13, which regulates the mo tion of the jack, and prevents the main arbor from turning too fast by the power ofthe weight. A wooden pulley E is fixed on the main arbor on the outside of the frame, for the endless chain e,which gives motion to the spit, and the pulley has several grooves to receive chains for two or more spits at the same time. Two legs or standards 1, h are rivetted to the frame G, to fix the jack against the wall over the fire place.
The weight for giving motion to the jacks is generally suspended by a pair of blocks, with two or three sheaves. The end of the line, or fall from the pulleys, is wound on the barrel A; and the weight is usually placed outside the house, and contained in a sort ofa chimney, to defend the lines of the pulleys from the weather. When pulleys are used, the jack will continue its motion longer without winding, but the weight must be much heavier than if it was simply suspended to the end of the cord.
When the weight is run down, a handle is applied to the square part a of the arbor of the barrel A, which pro jects through the frame H. By turning the handle round, the barrel goes with it and winds the rape upon its circum ference; but as the barrel slips round on the main arbor when the barrel is turned in that direction, the wheel B continues to revolve and early the spit by the momentum of the flywheel ll as lung as is requisite to wind up the weight.
A efiring Jack is strewn in Fig. 4. From the figure of the external case of this kind of jack it is called a bottle No spit is used with this jack, but the meat is sus pended befot e the fire, and the jack keeps it constantly in motion, by turning it round, first in one direction, and then back again ; for this purpose the jack is hung upon an arm, projecting from the arch over the fire-place by the loop q, ut the upper end of the bottle, and the meat is suspended to the hook fixed to a small axis L m, which is kept in con stant motion by the wheel-work within the bottle, and the motion is govetned by the fly-wheel O.
The spir..l spring it, coiled up into a box, which is mark ed A in the Figure, and is fastened to the frame. The in terior end of the spiral spring is connected with the main arbor B, which is supported by the plates R, S. On this arbor the w heel C with its ratchet-wheel Z is fixed, and turns the small pinion I) on the second arbor E; at the end of this arbor, the contrate or escape-wheel F is fixed ; and G is a vet tical arbor with two pallets a and b projecting from it, the one engaging in the teeth on the upper side of the contrate-wheel, and when the pallet a is not in action, the pallet b intercepts the lower teeth of the wheel. This is a crown-wheel escapement, such as is used in common watches, and gives motion to the arbor G alternately in a backwards and forwards direction. On the lower end of the arbor G a sector C is fixed, and is cut into teeth at its eircumference, to form a segment or portion of a wheel.
It gives motion to the pinionil on the short vertical arbor d; and the wheel I is fixed on the same arbor, to give motion to the pinion I.., in the centre of the jack, which is fixed on the vertical arbor au, that passes through the bottom plate of the bottle, and has the fly-wheel 0 fixed to it, with the hook P for suspending the meat. The arms of the sector c are sufficiently extended to admit the arbor in between them. The arbor is sustained by the fixed cock i, and is also suspended by a number of small catgut strings going up through the centre of the jack to the top of the neck of the bottle, and attached to the cross pin r. These strings take off part of the weight of the meat which is suspended on the hook P, and diminish the friction on its collar. This effect is also partly produced by a small spiral wire spring r, coiled round the arbor, and bearing on the cock i.
The spring jack is wound up by the key Q, when ap plied to the square part a of the main arbor ; and in the act of winding, the great wheel C is not turned round by the ratchet wheel z, because the click fixed to the peat wheel slips over the sloping side of the teeth. To prevent the spring from breaking, a pinion n is fixed on the end of of the main arbor; beyond the plate it works into the wheel o, which turns upon a pin fixed into the side plate S of the frame. When the main arbor has made a sufficient number of revolutions to wind up the spring, the leaves of the pinion 71 come in contact with a part of the wheel o, which has no space in it, and this prevents the ar bor being turned any further, so as to endanger the break ing of the spring. The maintaining power of the spring, when wound up, gives motion, by the wheel C and pinion E, to the escape wheel F, the upper tooth of which meets with the pallet a, and carries it along with it, turning the vertical arbor round upon its pivots. This motion is com municated by means of the sector C to the pinion 1-1, and its wheel I, and thence to the sector pinion L, and the fly wheel, and consequently to the meat. The use of the wheel work CHL is to make the meat turn round several times before the tooth of the w heel escapes the pallet a, and then the tooth on the under side of the escape wheel meets with the pallet b. and turns the vertical arbor G and the fly wheel b:..ck again, in a contrary direction to that in which it was behoe turned by the pallet a, because the underside of the esc:4)k mem wheel is going in a contrary direction to the upi cr when the under tooth of the wheel escapes from pallet b, the pallet a comes into action again, and thus continuous motion is kept up, first in one direction for a few turns, then in the opposite direction, and so on, till the maintaining power of the spring becomes exhausted, when it must be wound up again by the key Q. The tube re sembling the neck of the bottle is to give length to the cat gut strings before mentioned, atul which, by their twisting and untwisting, perform nearly the same office as the pen dulum spring in a watch, and make the fly wheel return back readily. The bottom V of the bottle is screwed to a Haunch or projecting rim round the bottom of the bottle ; by removing these screws, and taking out the cross pin r in the top of the neck, which hold the strings, the frame• containing the wheel work may be withdrawn from the case .r, to be repaired or oiled as occasion may require. (J. F.)