A pivotal invention, the multi-tube boiler, was patented by Marc Sèguin in 1827, and first applied to a locomotive built for the Saint Etienne-Lyon Railway in Southern France. It accomplished two things:

• Provided more heating surface which creates more steam and creates it faster—thus increasing locomotive speeds.
• Led to the discovery that under pressure, steam can be reheated to temperatures higher than 212°. Also known as super-saturation, this led to high-pressure boilers—boosting power output—and opening the era of massive articulated locomotives.