Symner, Miles (d. 1686), clergyman, mathematician, astronomer, and military engineer, is of unclear parentage, but considering his education at TCD, he was probably of Anglo-Irish or English descent. He entered TCD as a scholar in 1626, where his studies prepared him for becoming a minister in the Church of Ireland, which brought him to the diocese of Elphin in 1633. Little is known about this phase of his life, but in his early studies and later clerical life he is unlikely to have seen much experience in mathematics, including ballistics, fortifications, and probably architecture. Nothing is known about the circumstances under which he made the transition from clergyman to become chief engineer in Ireland in 1648. In that year, he articulated his thoughts about learning through experimentation in contrast to the century-old philosophical approaches to science. He was then engaged in astronomical observations and had made a quadrant of six-foot (1.83 m) radius, leading him to fix the latitude of Dublin at 53 degrees and 20 minutes.
Together with the engineer William Webb he served in the train of artillery headed by Roger Boyle (qv), then Lord Broghill (later earl of Orrery). Symner was ordered to execute repairs to Athlone castle in 1651, and two years later he and two others were detailed to select garrison buildings and castles for demolition in Connacht and Clare, and those remaining along the Shannon. This commission showed his ability to undertake strategic military planning for the Cromwellian regime to subdue this part of the country through a network of strongholds. Carrying the rank of major, he oversaw the demolition of castles as part of this military scheme. Considering the large number of fortifications that were built or repaired in Ireland from 1651 to 1656, it seems very likely that he became involved with military engineering works during this period, but the precise details remain unclear.
His knowledge of military engineering, and the mathematics associated with it, prepared him for his next position, the professorship of mathematics at TCD, to which he was appointed in 1652. His lectures are likely to have included the scientific aspects of land surveying, because in the following year he was member of a committee to inquire into the survey of Connacht and Clare, the area of Ireland with which he was most familiar. His scholarly communications extended to England when he became the pivotal Irish member of the Samuel Hartlib circle, which had been responsible for the founding of the Royal Society in England. His acquaintances in this scholarly community included Arnold (qv) and Gerald Boate (qv), William Petty (qv), Benjamin Worsley (qv), and Robert Boyle (qv), all of whom were proponents of the new scientific principles expounded in the New Learning. These activities provided the germ from which the Dublin Philosophical Society sprang in 1683.
With the restoration of Charles II as king in 1660, Symner lost his professorship at TCD, and temporarily reverted to a clerical career as archdeacon, successively of Clogher (1661) and Kildare (1668). His architectural skills must have made him a person in demand during this period of widespread building activity, when the country became more stable and wealthy. He can be identified with the ‘Mr Sumner’ who in 1662 and 1664 supervised building projects of the 2nd earl of Cork (qv) at Lismore Castle, Co. Waterford, which most likely included a classical portico, a novelty for Ireland at this time. In 1669 he was one of the committee to advise the dean and chapter of St Patrick's cathedral, Dublin, on repairs of the structure. In the following year he acted as overseer of the building of the oval St Andrew's church in the same city, then being constructed by the architect William Dodson. Symner was reappointed as lecturer of mathematics at TCD in 1668. Little is known about his activities over the next eighteen years before his death at TCD in 1686. He is not known to have published any of his scholarly endeavours, and he is not known to have completed his ambitious plan to write those sections for Ireland's naturall history that had not been completed by its author, Gerard Boate. The absence of written records from Symner's hand, however, should not detract from Symner's place in the early annals of scientific advances in seventeenth-century Ireland.