Until about 1800, the most common pattern of steam engine was the beam engine, built as an integral part of a stone or brick engine-house, but soon various patterns of self-contained portative engines (readily removable, but not on wheels) were developed, such as the table engine. Further decrease in size due to use of higher pressure came towards the end of the 18th century when the Cornish engineer, Richard Trevithick and the American engineer, Oliver Evans, independently began to construct higher-pressure (about ) engines which exhausted into the atmosphere, although Arthur Wolf working at the Meux Brewery in London was already experimenting with higher-pressure steam, in his efforts to save coal. This allowed an engine and boiler to be combined into a single unit compact and light enough to be used on mobile road and rail locomotives and steam boats.