During the first weeks of 1804, Richard Trevithick was engaged in building steam engines for Samuel Homfray at his Penydarren Ironworks in Merthyr Tydfil.
Within days of completing an engine fit for hammering and pumping Trevithick was writing letters to say how he was fitting it with wheels and adapting it to steam on the Merthyr tramroad.
In February 1804 Trevithick carried out the first trials of his Penydarren Locomotive on the cast iron rails of the tramroad.
“Last Saturday, we lighted the fire in the Tram Waggon and worked it without the wheels to try the engine…
“Monday we put it on the Tram Road. It worked very well and ran up hill and down with great ease… we have plenty of steam and power,” wrote Trevithick.
A few days later Trevithick writes wrote about more extensive trials. His new locomotive had steamed two miles along the rails of the tramroad – this would have been as far as Pentrebach – and back. The engine had hauled a load of ten tons in wagons.
“The Tram Waggon has been at work several times. It works exceeding well and is much more manageable than horses,” boasted Trevithick.
“The public is much taken with it.”
Trevithick said that he was planning to make a smaller locomotive to pull wagons on the tramroad.
“I intend to make a smaller engine for the road as this has much more power than is wanted here. This engine is to work a hammer.”
Trevithick also writes about a bet between ironmasters in Merthyr Tydfil – his own patron Samuel Homfray of the Penydarren Ironworks one of them. He said that the stakes were 500 guineas.