on astronomical subjects, written in 1654 and 1655, are printed in ‘Excerpta ex Literis ad Hevelium’ (Danzig, 1683, 4to). A third letter, dated 2 Feb. 1662–3, is preserved in Brit. Mus. Addit. MS. 28104, f. 10.
After the outbreak of the civil war Cambridge early suffered for its loyalty. In 1643 Samuel Ward was imprisoned in St. John's College, and Seth assiduously attended him until his death on 7 Sept. Seth was a staunch churchman, and, with Peter Gunning [q. v.], John Barwick [q. v.], and Isaac Barrow (1614–1680) [q. v.], he assisted in compiling ‘Certain Disquisitions and Considerations representing to the Conscience the Unlawfulness of the … Solemn League and Covenant.’ The first edition was immediately seized and burned by the puritans, and the earliest extant is that which appeared at Oxford in 1644. Deprived of his fellowship by the committee of visitors in August 1644 for refusing the covenant, he took refuge with Samuel Ward's relatives in and around London, and afterwards with Oughtred at Albury. While with him he improved his knowledge of mathematics, and on leaving his house took up his abode with his friend Ralph Freeman at Aspenden, his birthplace, acting as tutor to Freeman's sons. There he remained till 1649, when he paid a visit of some months' duration to Lord Wenman [see Wenman, Thomas, second Viscount] at Thame in Oxfordshire. In 1647 the visitation of Oxford University began. Among those ejected in 1648 was John Greaves [q. v.], Savilian professor of astronomy. On Greaves's recommendation, with the support of Scarburgh and Sir John Trevor, Ward was appointed his successor in 1649. He had by this time sufficiently mastered his scruples to take the oath to the English Commonwealth, and turned his attention to reviving the interest in the astronomical lectures, which had fallen into neglect and almost into disuse. He also gained fame as a preacher, though as a Savilian professor he was exempted from any obligation to the university to deliver discourses from the pulpit.
Ward is chiefly remembered as an astronomer by his theory of planetary motion. In 1645 Ismael Boulliau, in his ‘Astronomia Philolaica,’ enunciated an astronomical system in which for the first time the elliptical nature of the planetary orbits was taken into account. In 1653 Ward published a treatise entitled ‘In Ismaelis Bullialdi Astronomiæ Philolaicæ Fundamenta Inquisitio Brevis’ (Oxford, 4to), in which he advanced a theory of planetary motion at once simpler and more accurate than that of the French astronomer, and in 1656 he issued his ‘Astronomia Geometrica; ubi Methodus proponitur qua Primariorum Planetarum Astronomia sive Elliptica sive Circularis possit Geometrice absolvi,’ in which he propounded it in a more elaborate and finished form. According to his hypothesis the line drawn from a planet to the superior focus of its elliptical orbit turns with a uniform angular velocity round that point. In orbits of small eccentricity this is nearly true, and in such cases the result almost coincides with that obtained by applying Kepler's principle of the uniform description of areas. Ward, however, regarded his theorem as universally true, guided by the belief that a centre of uniform motion must necessarily exist. His was the last system involving such an assumption which had any vogue, and it was abandoned as simpler methods were found for resolving Kepler's problem. Boulliau replied to him in ‘Ismaelis Bullialdi Astronomiæ Philolaicæ Fundamenta clarius explicata et asserta,’ printed in his ‘Exercitationes Geometricæ tres’ (1657), acknowledging some errors of his own and pointing out some inaccuracies in Ward's theory.
On 23 Oct. 1649 Ward was incorporated M.A. at Oxford, and he entered himself as a fellow-commoner on 29 April 1650 at Wadham College from regard for the warden, John Wilkins [q. v.], famous for his learning. During his residence in Oxford he lived at Wadham, in the chamber over the gate. At that time Oxford was the home of many illustrious men of science, among others of Robert Boyle [q. v.], Thomas Willis (1621–1675) [q. v.], Jonathan Goddard [q. v.], John Wallis (1618–1673) [q. v.], Ralph Bathurst [q. v.], and Lawrence Rooke [q. v.] These men constituted a brilliant intellectual society, and vastly assisted the progress of science in England. In 1645 Wallis, Goddard, Theodore Haak [q. v.], and others, then in London, held weekly meetings to discuss mathematics and physical science. About 1649, when most of them had removed to Oxford, they formed ‘The Philosophical Society of Oxford,’ of which Ward became a member. There still remained a remnant of the parent society, however, in London, meeting generally in Gresham College, and from these two associations the Royal Society afterwards sprang. It was incorporated by charter on 15 July 1662, and received a more ample constitution on 22 April 1663. Ward, who by that time had removed to London, was one of the original members.
During his residence at Oxford Ward became involved in a mathematical and philosophical controversy with Hobbes, in which, however, Wallis, the Savilian professor of geometry, took the chief share. In 1654 Ward, replying in his ‘Vindiciæ Academiarum’ to
