The aim of model engineering to build mechanical models is now usually purely recreational, although beginning with the Industrial Revolution in the late 18th century through to the late 20th century such models were widely produced as aids to technical education, either as apprentice projects or as classroom or public institutional exhibits. They were also produced as commercial props to support a patent, to visualise a proposed capital venture, or to advertise a manufacturer's trade. Many museums in the old industrialised countries house original collections of mechanical models stemming from the earliest days of the industrial revolution. One of the earliest known models of a steam engine, that of a Newcomen beam engine, was made prior to 1763. The Science Museum, London published catalogues illustrating many early models. Many of these models represent the same subjects that remain popular with model engineers today, which attests to the long tradition of model engineering.