The Newcomen engine was used to drain mines, from the outset of its invention around 1710. When this was a coal mine, supplying it was not difficult, as the "small " coal that was hard to gather up and transport could be used for fuel. But if it was not a coal mine, this was quite expensive, so non-coal mines ( like the Cornish tin mines) would not be driven to use steam engines until after 1741, when they were desperate. A Newcomen engine was pretty inefficient: it dumped a great deal of useful heat on every stroke, so keeping it fed was expensive. Boulton and Watt would later lease their engines for a third of the value of the amount of the coal a mineowner would save, using their engine over a Newcomen one.