Gregory wrote _Hints for the Use of Teachers of Elementary Mathematics_ (1840, new edition 1853), and _Mathematics for Practical Men_ (1825), which was revised and enlarged by Henry Law in 1848, and again by J. R. Young in 1862. His _Letters on the Evidences of Christianity_ (1815) have been several times reprinted, and an abridgment was published by the Religious Tract Society in 1853. He will probably be longest remembered for his _Biography of Robert Hall_, which first appeared in the collected edition of Hall's works, was published separately in 1833, and has since passed through several editions. The minor importance of his _Memoir of John Mason Good_ (1828) is due to the narrower fame of the subject. Gregory was one of the founders of the Royal Astronomical Society. In 1802 he was appointed editor of the _Gentlemen's Diary_, and in 1818 editor of the _Ladies' Diary_ and superintendent of the almanacs of the Stationers' Company. GREIFENBERG, a town of Germany, in the Prussian province of Pomerania, on the Rega, 45 m. N.E. of Stettin on the railway to Kolberg. Pop. (1905) 7208. It has two Evangelical churches (among them that of St Mary, dating from 13th century), two ancient gateways, a powder tower and a gymnasium. The manufacture of machines, stoves and bricks are the principal industries. Greifenberg possessed municipal rights as early as 1262, and in the 14th and 15th centuries had a considerable shipping trade, but it lost much of its prosperity during the Thirty Years' War. See Riemann, _Geschichte der Stadt Greifenberg_ (1862). GREIFENHAGEN, a town of Germany, in the Prussian province of Pomerania, on the Reglitz, 12 m. S.S.W. of Stettin by rail. Pop. (1905) 6473. Its prosperity depends chiefly on agriculture and it has a considerable trade in cattle. There are also felt manufactures and saw mills. Greifenhagen was built in 1230, and was raised to the rank of a town and fortified about 1250. In the Thirty Years' War it was taken both by the imperialists and the Swedes, and in 1675 it was captured by the Brandenburgers, into whose possession it came finally in 1679.