PRISM n.
xis. See Form, n., 13. Achromatic prism (Opt.), a prism composed usually of two prisms of different transparent substances which have unequal dispersive powers, as two different kinds of glass, especially flint glass and crown glass, the difference of dispersive power being compensated by giving them different refracti…
PULLEY n.
with a broad rim, or grooved rim, for transmitting power from, or imparting power to, the different parts of machinery, or for changing the direction of motion, by means of a belt, cord, rope, or chain.
PUNCH n.
A tool, usually of steel, variously shaped at one end for different uses, and either solid, for stamping or for perforating holes in metallic plates and other substances, or hollow and sharpedged, for cutting out blanks, as for buttons, steel pens, jewelry, and the like; a die.