Dicuil, also an Irish monk, was the author of a remarkable work on geography, _De Mensura Provinciarum Orbis Terrae_, which was written in 825, and contains interesting references to Iceland and especially to the navigable canal which once connected the Nile with the Red Sea. He wrote between 814 and 816 a work on astronomy which has never been published. It is probable, but not certain, that he belonged to Clonmacnois. Dungal, like the two others named above, was an astronomer. He probably belonged to Bangor, and left his native land early in the ninth century. In 811 he wrote a remarkable work, _Dungali Reclusi Epistola de duplici solis eclipsi anno 810 ad Carolum Magnum_. This letter, which is still extant, was written at the request of Charlemagne, who considered its author to be the most learned astronomer in existence and most likely to clear up the problem submitted to him. Before passing to the next period, a word should be said as to the medieval physicians, often if not usually belonging to families of medical men, such as the Leahys and O'Hickeys, and attached hereditarily to the greater clans. These men were chiefly compilers, but such works of theirs as we have throw light upon the state of medical knowledge in their day. Thus there is extant a treatise on _Materia Medica_ (1459); written by Cormac MacDuinntsleibhe (Dunleavy), hereditary physician to the clan of O'Donnell in Ulster. A more interesting work is the _Cursus Medicus_, consisting of six books on Physiology, three on Pathology, and four on Semeiotica, written in the reign of Charles I. of England by Nial O'Glacan, born in Donegal, and at one time physician to the king of France. O'Glacan's name introduces us to the middle period, if indeed it does not belong there. _Inter arma silent leges_, and it may be added, scientific work. The troublous state of Ireland for many long years fully explains the absence of men of science in any abundance until the end of the eighteenth century. Still there are three names which can never be forgotten, belonging to the period in question. Sir Hans Sloane was born at Killileagh, in Ulster, in 1660. He studied medicine abroad, went to London where he settled, and was made a Fellow of the Royal Society. He published a work on the West Indies, but his claim to undying memory is the fact that it was the bequest of his most valuable and extensive collections to the nation which was the beginning and foundation of the British Museum, perhaps the most celebrated institution of its kind in the world. Sloane's collection, it should be added, contained an immense number of valuable books and manuscripts, as well as of objects more usually associated with the idea of a museum. He died in 1753.