296 GLOSSARY. 



Tumbler, a latch in a lock, wliicli, by means of a spring, detains the 

 holt in its place until lifted by the key. 



Tumbling rod, the rod which connects the motion of a horse-power 

 Avith tliat of a thrashing or other machine. 



Turbine wheel, a horizontal water-wheel, so constructed that the 

 current strikes all the floats or buckets around the circumference at the 

 same time, thus imparting to it great power for its size. It is sub- 

 merged, the water escaping towards the centre and below, or above and 

 below together. 



Undershot wheel, a water-wheel moved by the current striking 

 against the lower portion of its circumference. 



Universal joint, a connecting joint between two rods, consisting of 

 a sort of double hinge, admitting motion in any direction. 



Valve, a lid for closing an aperture or passage, so as to open only in 

 one direction. 



Velocity, speed or swiftness ; which may be uniform, or equal 

 throughout ; accelerated^ or increasing ; or retarded^ or rendered slower. 



Virtual velocities, Principle of, tliat by which certain powers are 

 equal to each other, where tlie force and space moved over, whatever 

 these may be, are the same when multiplied together. 



Washer, a circular piece of metal, pasteboard, or leather, placed be- 

 low a screw-head, or nut, or within a liuch-pin, for protection. 



Water-ram, see Ram. 



Whiffle-tree, or Whipple-tree, the cross-bar to which the traces 

 of a horse are attached ; see Single-tree, 



WiiiP-SAW, a large saw, worked by a man at one end, with a wooden 

 spring at the other ; a cross-cut saw. 



Winch, a bent handle or right-angled lever, for turning a wheel or 

 grindstone, or producing rotary motion for otlier purposes. 



Windlass, a machine for raising heavy weights, by the winding of a 

 rope or chain on a horizontal axle, and turned by a winch or by levers. 



WiNROw, or Windrow, the ridge of hay raked up on a meadow. 



Wrest, a partition which determines the form of the bucket in an 

 overshot wheel. 



