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Olinthus Gilbert Gregory (1744-1841) was an English mathematician.
1744 He was born on the 29 January, at Yaxley in Huntingdonshire.
1793 Having been educated by Richard Weston, a Leicester botanist, he published a treatise, Lessons Astronomical and Philosophical.
1796 Having settled at Cambridge, Gregory first acted as sub-editor on the Cambridge Intelligencer, and then opened a booksellers shop.
1802 He obtained an appointment as mathematical master at the Royal Military Academy, Woolwich, through the influence of Charles Hutton, to whose notice he had been brought by a manuscript on the Use of the Sliding Rule. He was appointed editor of the Gentlemen's Diary.
1807 Hutton resigned and Gregory succeeded him in the professorship.
1813 Gregory was a co-editor of Pantologia.
1815 He wrote Letters on the Evidences of Christianity.
1818 He became editor of the Lady's Diary and superintendent of the almanacs of the Stationers Company
1824 Professor of Mathematics at the Royal Military Academy, Woolwich 
1824 'Velocity of Sound' 
1824 Olinthus Gregory, became a member of the Institution of Civil Engineers.
1825 Gregory wrote Mathematics for Practical Men.
1833 His Biography of Robert Hall, which first appeared in the collected edition of Hall's works, was published separately.
1838 Failing health obliged him to retire.
1840 Gregory wrote Hints for the Use of Teachers of Elementary Mathematics.
Gregory was one of the founders of the Royal Astronomical Society.
Gregory's son was Charles Hutton Gregory who later became president of the Institution of Civil Engineers
1841 Olinthus Gilbert Gregory died at Woolwich on 2 February.
1842 Obituary 
Dr. Gregory was born at Yaxley, in Huntingdonshire, in 1774, and showed, even in his boyhood, that aptitude for study which marked his subsequent life.
His literary career commenced at an unusually early age, by mathematical and philosophical contributions to the periodicals of the time, and at nineteen his first work, 'Lessons Astronomical and Philosophical, for the Instruction of Youth,' was published.
He shortly after removed to Cambridge, where he became an eminent teacher of mathematics, but did not enter the University.
In 1802, aided by the influence and friendship of Dr. Hutton, he was appointed one of the Mathematical Masters at the Royal Military Academy at Woolwich, and in 1821, he was raised to the Professor’s chair, then vacant by the death of Professor Bonnycastle.
It would be tedious to enumerate the many excellent works of which Dr. Gregory was author or editor, they are all remarkable for a depth of science, and a variety of knowledge imparted in the most simple manner.
Our profession is essentially indebted to him for his 'Mathematics for practical Man'. This work, which he dedicated to the Institution, is too well known among us to require remark or eulogium.
Dr. Gregory was one of the founders of the Astronomical Society, and officiated for many years as its Secretary ; he was also a Member of many of the learned Societies of Europe.