Francis, born 24 April 1617, was acting in 1643 as captain at Poole, and took part in a notable defence of Poole against an attempt of the royalists, under the Earl of Crawford, to obtain possession of the town by treachery, when the royalists suffered a severe repulse. He was killed in battle, 9 Feb. 1644–5 (Rushworth, Collections; Whitelocke, Memorials, pp. 116).
John, the sixth son, born 26 Feb. 1626–7, served under his brother William, took part in the war in Ireland, became major of Sir Arthur Hesilrigge's regiment of horse and governor of Stirling, and was mortally wounded in a skirmish with the Scots in April 1651 (Mercurius Politicus, 6–13 March, 17–24 April, 1651).
Richard, the youngest son, is described as ‘captain’ in the register of his death, but his military services cannot be traced. He had important civil employment under the Commonwealth as trustee of crown rents (Green, Cal. State Papers, Dom. 1655 and 1655–6, passim), and was buried on 27 Jan. 1657.
A tragic fate overtook Sydenham's mother, who was killed in Dorset in July 1644 by the royalist Major Williams under unknown circumstances [see under Sydenham, William].
Sydenham entered Magdalen Hall, Oxford, as a fellow-commoner on 20 May 1642. His stay in the university cannot have exceeded a few months, as the civil war broke out in August of that year. Leaving Oxford for his native county, he engaged in military service with the parliamentary forces there, according to the positive statements of at least two contemporaries—Sir Richard Blackmore (Treatise on the Small-Pox, preface) and Dr. Andrew Broun (A Vindicatory Schedule, &c., Edinburgh, 1691, p. 81, quoted in Dr. John Brown's Horæ Subsecivæ, 1858, p. 461). Moreover, in a petition in Sydenham's own handwriting, preserved in the record office, Sydenham states explicitly that he served the parliament faithfully, and suffered much loss of blood. Sydenham's military service began in 1642 in his native county. The importance and zeal of his family procured for him at once a commission as captain of horse. He seems to have been at Exeter when the town was taken by the royalists on 4 Sept. 1643, and was a prisoner for nine or ten months from that date. He must have been concerned with his brothers in several other operations, though in one instance only can his name be traced. In July 1644 we find that Colonel and Major Sydenham, with their forces, repulsed a royalist attack on Dorchester from Wareham with great success, and in this engagement ‘Captain’ Sydenham, who had been prisoner a long time to the royalists in Exeter, behaved himself very bravely (Hutchins, History of Dorset, 3rd ed. ii. 344). This could be no one else than Thomas Sydenham, since his next brother, John, was not yet eighteen. His military service ceased in the autumn of 1645, when the royal garrisons in Dorset were finally reduced by Fairfax and Cromwell.
When Oxford and the other royal garrisons surrendered in 1646, the war was virtually at an end, and Sydenham resigned his commission. On his way to London in order to return to Oxford, from which the troubles of the first war had so long separated him, he chanced to meet with Dr. Thomas Coxe [q. v.], who was attending his brother; and it was by his advice that he was induced to apply himself to medicine (Observationes Medicæ, 1676, dedication to Mapletoft). In a letter of later date to Dr. Gould (Sloane MS. 4376, Brit. Mus.), Sydenham says that he entered Wadham College in the year in which Oxford was surrendered, meaning, as the college register shows, 1647, when the university was taken possession of by the parliamentary visitors. On 14 Oct. 1647 he became a fellow-commoner of Wadham (Gardiner, Registers, 1889, i. 165). The name ‘Sidnam’ appears among the M.A.'s of Magdalen Hall (4 May 1648) as submitting, but perhaps does not refer to Thomas Sydenham. Sydenham was appointed one of the visitors' delegates on 30 Sept. 1647. On 3 Oct. 1648 he was elected by the visitors to a fellowship in All Souls' College; and on 29 March 1649 he was appointed senior bursar of the college (Burrows, Visitation of Oxford, p. 566).
Sydenham's medical degree was obtained in a somewhat irregular manner. He was created bachelor of medicine on 14 April 1648 by command of the Earl of Pembroke, chancellor of the university, without having taken a degree in arts (Wood, Athenæ, ed. 1721, ii. 639; Fasti, pp. 63–5). He must at some time later have become M.A., since he is so styled in the archives of the College of Physicians. As Sydenham had been only six months resident in the university, his medical degree would have been rather the starting point than the goal of his medical studies. He himself says that after a few years spent in the university he returned to London for the practice of medicine (Obs. Med. loc. cit.). There is, however, reason to believe that his studies were interrupted by a second period of military service. He resigned his fellowship in 1655 (All Souls' Archives, ed. C. T. Martin, London, 1877, p. 381).
