GLOSSARY. 295 



Subsoil-plow, a plow running? below the furrow of a common plow, 

 for breaking; up or loosening the subsoil or lower soil of a field. 



Swage, to give shape to a substance by stampiug with a die. 



SwEEP-POWEK, a horse-power for driving thrashing and other ma- 

 chines, where the horses are attached to a pole and walli in a circle. 



Swingle-tree, also called swing-tree, single-tree, whipple-tree, 

 and WHIFFLE-TREE ; the cross-bar to which traces are attached. 



Swing-plow, a plow with no wheel under the beam. 



Swivel, a ring and axis in a chain, to admit of its turning. 



Swivel bridge, a bridge which turns round sideways on its centre. 



Swivel plow, a side-hill plow, or a plow with a reversible mould-board. 



Tackle, a pulley, or machine with ropes and blocks for raising heavy- 

 weights. 



Tail-race, the channel which carries off the water below a water 

 wheel. 



Tedder, a machine for turning and spreading hay. 



Thill, one of the shafts of a wagon between which the horse is put 

 often corrupted to Fill. 



Throttle-valve, a valve which turns at its centre on an axis gener- 

 ally used to regulate the supply of steam to the cylinder of a steam-en- 

 gine. 



Thumb-screw, a screw with its head flattened in the direction of its 

 length, so as to be turned witli the thumb and finger. 



Tide-wheel, a wheel adapted to currents flowing both ways the float- 

 boards pointing from the centre. 



Tine, the tooth or prong of a fork. 



Tire, the iron band which binds together the fellies of a wheel. 



Toggle-joint, or knee-joint, a mechanical power exerted by straight- 

 ening a double bar with a hinge at the middle or connection. 



Torsion, the act of twisting by the application of lateral force. The 

 force of torsion is the elasticity of a twisted body. 



Track-cleaner, an attachment to a mowing machine, to throw the 

 cut grass away from that wliich is uncut. 



Traction, Angle of, the angle between the line of draught and any 

 given plane, as that of the earth's surface. 



Trammel, an instrument used by carpenters for drawing an ellipse. 



Tread-power, a machine on which the horse or other animal working 

 it wallvs. It may be either a horizontal or slightly inclined wheel; or 

 an endless-chain power, the term being more frequently applied to the 

 latter. 



Trench-plow, a plow cutting deep furrows and bringing the subsoil 

 up to the surface; as distinguished from a subsoil plow, which only 

 loosens the subsoil and leaves it below the surface. 



Trundle-head, a wheel turniiig a mill-stone. 



Tub-wheel, a horizontal water-wheel, driven by the percussion of the 

 stream against its floats, and not submerged in water. 



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