MacMahon, Bernard (c.1736–1816), priest, scientist, and translator, was born at Castlering, Co. Louth, one of two brothers. He was educated locally and studied for the secular priesthood at Antwerp, presumably at the Irish College there. His name appears on the 1771 list of Irishmen awarded arts degrees from the University of Louvain. His knowledge of French and Latin contributed to his later work as a translator.
The date and place of his ordination and the record of his services in his native diocese of Armagh after his return to Ireland are not known. From 1780 he came into prominence as an editor of catholic publications in Dublin; he had edited the first missal printed in Ireland in 1777. He edited several editions of the New Testament and many catholic publications including Alban Butler's lives of the saints. He is also said to have edited one or two mathematical books. He translated several catholic books and in 1791 oversaw a translation of the Bible. In 1795 he was appointed a canon of the Dublin diocese.
His record of scientific work largely relates to the observation and measurement of tides in Dublin port and harbour. In 1789 he was involved in the construction of a nautical observatory at the Pigeon House to measure tidal height and velocity. In 1801 he was permitted to fix an apparatus of his own design at the Poolbeg lighthouse, which determined high or low tide and set off a signal to notify shipping of the state of the tide. Before this advance many ships were lost in the bay, due to lack of knowledge of tides and movement of water over the sand bars. After advising the government of the need to survey the bathymetry of the bay, he spent three years surveying from a yacht and in the process was the first person to compile tide tables for the port. These were adopted by the commissioners of the Custom House and of the Coast-office and were included in several Dublin almanacs from 1808 up to his death. He lived in Hardwicke St., where he had taken on the lease of the chapel on Dorset St. in 1804, after the departure of the Poor Clares to Harold's Cross. He remained there as chaplain until his death on 20 September 1816. He was buried in Inniskeen, Co. Monaghan, and an inscribed stone was erected to his memory by his niece. He was remembered as a cheerful person, full of anecdotes and with liberal views of religion.