Coal gas was introduced to Great Britain as an illuminating gas by William Murdoch (August 21,1754 - November 15, 1839) a Scottish engineer and inventor who worked for Boulton & Watt. In the early 1790s, he began experimenting with various types of gas, finally settling on coal gas as the most effective. He created a process wherein the coal was gasified by heating the coal in enclosed ovens with an oxygen-poor atmosphere. Samuel Clegg (1781- 1861) was a British civil engineer. He was apprenticed to Boulton and Watt, and witnessed many of Murdoch's experiments in the use of coal gas. Clegg was hired by Henry Lodge to adapt the new lighting system to his cotton mills, and finding the necessity for a simpler method of purifying the gas, he invented the lime purifiers. Boulton and Watt contributed the basic design of the retort, condenser, and gasometer, while Clegg improved the gasometer and introduced lime purification and the hydraulic main, another purifier.