DR. DUNCAN, professor of mathematics and of medicine in the university of Helmstadt, was born in the year 1561 at Aberdeen, where he received the first part of his education in languages and philosophy. About the age of eighteen he repaired to the university of Francfort, where he spent three years in a diligent application to mathematics and philosophy. From Francfort he proceeded to Wratislaw, or Breslau, in Silesia, where he is said to have made uncommon progress in his favourite study of mathematics, under the direction of a very eminent professor, Paulus Wittichius. Having studied at Breslau for the space of one year, he returned to Francfort and remained there three years, paying the most intense application to the study of physic. A contagious distemper having broken out at that place, the students were dispersed, and Liddel retired to the university of Rostock. Here he renewed his studies, rather as a companion than as a pupil of the celebrated Bruceus, who, though an excellent mathematician, did not scruple to confess that he was instructed by Liddel in the more perfect knowledge of the Copernican system, and other astronomical questions. In 1590 he returned once more to Francfort. But having there heard of the increasing Liddel, creasing reputation of the Academia Julia, established at Lidford. Helmstadt by Henry duke of Brunswick, Mr Liddel removed thither; and soon after his arrival was appointed to the first or lower professorship of mathematics. From thence he was promoted to the second and more dignified mathematical chair, which he occupied for nine years, with much credit to himself and to the Julian Academy. In 1596 he obtained the degree of M.D., was admitted a member of that faculty, and began publicly to teach physic. By his teaching and his writings he was the chief support of the medical school at Helmstadt; was employed as first physician at the court of Brunswick, and had much practice among the principal inhabitants of that country. Having been several times elected dean of the faculties both of philosophy and physic, he had in the year 1604 the honour of being chosen protector of the university. But neither academical honours, nor the profits of an extensive practice abroad, could make Dr Liddel forget his native country. In the year 1606 he took a final leave of the Academia Julia; and after travelling for some time through Germany and Italy, he at length settled in Scotland. He died in the year 1613, in the 52d year of his age. By his last will be bestowed certain lands purchased by him near Aberdeen upon the university there, in all time coming, for the education and support of six poor scholars. Among a variety of regulations and injunctions for the management of this charity, he appoints the magistrates of Aberdeen his trustees, and solemnly denounces the curse of God on any person who shall abuse or misapply it. His works are, 1. Disputationes Medicinales, Helmstadt, 1603, 4to. 2. Ars Medica succincte et perspicue explicata, Hamburghii, 1607, 8vo. This performance is dedicated to King James VI. and is divided into five books, viz. Introductio in totum Medicinam; De Physiologia; De Pathologia; De Signorum doctrina; De Therapeutica. 3. De Febribus Libri tres, Hamburghii, 1610, 12mo. 4. Tractatus de dente aureo, Hamburghii, 1628, 12mo. This last performance Dr Liddel published in order to refute a ridiculous story then current of a poor boy in Silesia, who, at seven years of age, having lost some of his teeth, brought forth, to the astonishment of his parents, a new tooth of pure gold. Jacobus Horstius, doctor and professor of medicine in the Academia Julia, at the same time with our author, had published a book, which he dedicated to the emperor Rudolphus II. to prove that this wonderful tooth was a prodigy sent from heaven to encourage the Germans then at war with the Turks, and foretelling, from this golden tooth, the future victories of the Christians, with the final destruction of the Turkish empire and Mahometan faith, and a return of the golden age in 1700, preparatory to the end of the world. The imposture was soon after discovered to be a thin plate of gold, skilfully drawn over the natural tooth by an artist of that country, with a view to excite the public admiration and charity. 5. Artis conservandi Sanitatem, libri duo, Aberdoniae, 1651, 12mo; a posthumous work.