sentences:  When the constituency was established the vast majority of the electorate were resident in Merthyr Tydfil and its environs, such as the industrial township of Dowlais.In contrast the electorate of the neighbouring Aberdare Valley was relatively small, numbering 3,691 compared with 22,083 in Merthyr.The first member for Merthyr Tydfil was Sir Josiah John Guest who served, albeit with some opposition until his death in 1852.