J A C 



600 



J A C 



Jack. 



PLATB 

 CCXCIX. 



Fig. 9. 



Roasting 



jack. 



Smoke jack. 

 lig. 5. 



Roasting 

 jack with a 

 weight. 

 Kig. 3. 



nected with the cylinder near its top; the other extremi- 

 ty of this pipe is carried to a small injecting pump C, 

 standing in the cistern R, and actuated by the lever H. 

 At each stroke of the pump a small quantity of water 

 is forced or injected into the large cylinder, and this 

 causes the piston B to rise through the collar of leather 

 a very small quantity each time. This quantity will bear 

 the same proportion to the motion given to the piston of 

 the pump C as the area of that piston bears to that of 

 the large piston B. The force applied to the small 

 pump, and that exerted by the great cylinder, will be 

 in the inverse proportion of these areas. * 



The pump rod is confined to a perpendicular motion 

 by an iron frame P, through which it passes. 



The top or head of the large cylinder is made larger 

 than the lower part, as shewn by the dotted lines, and 

 the shoulder which rests on the top of the block to sus- 

 tain the cylinder. When the weight or burden is to be 

 lowered down, it is done by opening a discharge valve in 

 the pump, the handle of which is seen at p : this allows 

 the water to return by the small copper pipe b, and 

 escape from the cylinder a into the pump cistern R. 

 When the power of the lever H is not found sufficient 

 to perform its work, it can be augmented, by taking 

 out the centre pin r, which forms the fulcrum of the 

 lever, and inserting it into another hole which is nearer 

 the centre of the pump. 



Roasting Jack, is a machine for turning round meat 

 when placed before the fire, so as to expose every part 

 of the surface to the heat. These jacks are constructed 

 in different ways ; and are either put in motion by 

 dogs, by the smoke which ascends the chimney, by a 

 weight, or by a spring. 



When a dog is employed, the spit on which the 

 meat is placed is mounted before the fire, and put in 

 motion by a wheel, in which the dog walks in the same 

 manner as men turn the walking wheel crane ; this 

 kind of jack is now out of use. 



A smoke jack is represented in Fig. 5. where A A is 

 the brickwork of the chimney, which is contracted to 

 a circular figure at AA ; B is a strong iron bar, placed 

 upon an arch of brickwork over the fire-place, to form 

 a support for the wheel- work of the jack ; C is a hori- 

 zontal wheel placed in the circular funnel A A ; it is made 

 of iron plate, with a number of vanes radiating from the 

 centre, each being placed at an angle of about 30 to the 

 plane of the wheel ; the heated air which ascends the 

 chimney will strike the vanes and turn the wheel ; the 

 lower end of the spindle D, on which the wheel is 

 fixed, has a pinion fixed on it, and turns a contrate 

 or crown wheel F on the horizontal spindle G ; on the 

 other end of this spindle is a pulley H, for an endless 

 chain, which descends to the spit on which the meat is 

 placed ; the pulley pinned on the end of the spit is laid 

 in the loop formed by the endless chain, so that this 

 chain at the same time suspends one end of the spit, 

 and gives motion to it ; the upper pivot of the spindle 

 D is supported in an iron bracket m, projecting from 

 the inside of the chimney, and the lower pivot rests on 

 the top of a standard n, which also carries one end of 

 the horizontal spindle G ; when the chimney requires 

 to be swept, the wheel C is lifted out of its centre, to 

 allow a boy to pass ; these jacks are always in motion 

 when the fire is kept up. 



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 up- 

 on the main axis, which is shewn by dotted lines: It slips 



round upon it quite freely in the direction proper for 

 winding up the weight ; 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 2L ? 

 fixed fast on the main arbor, and its teeth turn a pi- 

 nion 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 veif- 

 tical spindle T. On the top of the spindle is the fly- 

 wheel D, which regulates the motion of the jack, and 

 prevents the main arbor from turning too fast by the 

 power of the 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 I, K 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 gene- 

 rally 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 j and the weight is usually placed 

 outside the house, and contained in a sort of a chimney, 

 to defend the lines of the pulleys from the weather. 

 When pulleys are used, the jack will continue its mo- 

 tion 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 * of the arbor of the barrel A, which 

 projects through the frame H. By turning the handle 

 round, the barrel goes with it and winds the rope upon 

 its circumference ; 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 carry the spit by 

 the momentum of the fly-wheel D as long as is requi- 

 site to wind up the weight. 



A spring Jack is shewn in Fig. 4. From the figure Spring 

 of the external case of this kind of jack it is called a jack. 

 bottle jack. No spit is used with this jack, but the meat Fig. *. 

 is suspended before the fire, and the jack keeps it con- 

 stantly in motion, by turning it round, first in one di- 

 rection, 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, at 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 constant motion 

 by the wheel- work within the bottle, and the motion is 

 governed by the fly-wheel O. 



The spiral spring is coiled up into a box, which is 

 marked A in the Figure, and is fastened to the frame. 

 The interior end of the spiral spring is connected with 

 the main arbor B, which is supported by the plates R, S. 

 On this arbor the wheel C with its ratchet-wheel Z is 

 fixed, and turns the small pinion D on the second ar- 

 bor E ; at the end of this arbor, the contrate or escape- 

 wheel F is fixed; and G is a vertical 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 I 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 circumfe- 

 rence, to form a segment or portion of a wheel. It gives 

 motion to the pinion H on the short vertical arbor d; 

 and the wheel I is fixed on the same arbor, to give mo- 





* See the article HYDRODYNAMICS in this volume, p. 48?. 



