This document discusses several types of straight line mechanisms: - Watt's linkage, invented by James Watt in 1784, converts rotary or angular motion into near-perfect straight line motion. It was used in early steam engines. - The Sarrus linkage, invented in 1853 by Pierre Sarrus, converts limited circular motion into linear motion without guideways using a six-bar spatial linkage. - The Roberts linkage and Hoecken linkage, both four-bar linkages developed by Richard Roberts and Karl Hoecken respectively, convert rotational motion into approximate straight line motion.