Joseph Harris, elder brother of the methodist preacher Howell Harris, made important contributions to the sciences and public life of Great Britain in the eighteenth century. A protégé of Edmond Halley and an apprentice to globe and mapmakers, Harris made a lasting impression on some of the most illustrious scientists of his day, contributing to our understanding of astronomy, longitude, navigation, instrument making and optics. And, as assay master at the Royal Mint, he influenced the standardisation of weights and measures, and became a confident of politicians, Prime Ministers and Chancellors of the Exchequer. His essays on our monetary system still impact on political structures today. Remarkably, Harris also found time to make astronomical observations and teach navigational techniques for the Royal Society, and in 1761 was the only man in Wales to record the Transit of Venus.