292 GLOSSARY. 



Lever, a bar or rod for raisiuf? weights, resting on a point called a 

 fulcrum. 



Lever-power, see Sweep-power. 



Male screw, a screw with a spiral tliread, fitting into a hole with cor- 

 responding threads called a. female screw. 



Mechanical powers, the simple machines or elements of machinery, 

 consisting essentially of the Lever and Inclined Plane ; the lever com- 

 prising the Wheel and Axle and the Pulley, and the inclined plane com- 

 prising the Wedge and the Screw. 



MAsn, or Mesh, to interlock, as the teeth of cog-wheels. 



Mechanics, the science that treats of forces and powers, and their 

 action on bodies, and particularly as applied to the construction of ma- 

 chines. 



Mitre, to cut to an angle of 45 degrees, so that two pieces joined 

 shall make a right angle. 



Momentum, impetus ; the force of a moving body. 



Monkey, an apparatus for disengaging and securing again the ram of 

 a pile-engine. 



Mortise, a hole cut to receive the end or tenon of another piece. 



Nut, a piece of iron furnished with a screw-hole, used on the end of a 

 screw for securing tlie parts of machinery. 



Overshot wheel, a water-wheel, the circumference of which is fur- 

 nished with cavities or buckets, into which the stream of water is deliv- 

 ered at the top, turning the wheel by its weight. 



Pall, or Pawl, the catch of a ratchet-wheel ; a click. 



Pent-stock, an upright flume. 



Perambulator, a measurer of distances, consisting of a wheel, and 

 index to show by wheelwork the number of its turns. 



Percussion, Centre of, that point of a moving body at which its im- 

 petus is supposed to be concentrated. 



Pile-driver, or Pile-engine, an engine for driving piles into the 

 ground, effected by repeatedly dropping a heavy weight on the heads of 

 the piles; used mostly in swamp or water wlien the bottom is mud. 



Pinion, a small-toothed wheel, working in the teeth of a larger one. 



Pitch, the distance between the centres of two contiguous cog-wheels. 



Pitch line, the circle, parallel with the circumference, which passes 

 through the centres of the teeth of a wheel. 



Pitman, a rod connected with a wheel or crank, to change rotary to 

 reciprocating motion, or the reverse. 



Planet-wiieels, two elliptical wheels connected by teeth running 

 into each other, and revolving on their foci. 



Plow-beam, the main timber of a plow, by which it is drawn. 



Plow-share, the front part beneath the soil, which performs the cut- 

 ting sometimes (ivl\\{:.([ plow-nTioe, ov plow-point. 



Plunger, the piston of a forcing pump. 



Pneumatics, the science treating of the mechanical properties of air. 



Pole, the tongue of a reaping or other machine. 



