A system applied to steam engines whereby the steam was used twice, once in 'high pressure cylinders' at the pressure developed in the boiler and afterwards in 'low pressure cylinders' using the steam exhausted from the high pressure cylinders. The system was first tried on a locomotive of the UK Eastern Counties Railway in 1850 and later became popular for many locomotive designs world-wide. The Midland Railway was the chief exponent in the UK. It was sometimes referred to as 'continuous expansion'.