Thomson, Jordanus de Nemore and the Mathematics of Astrolabes: De Plana Spera (Toronto: Pontifical Institute of Mediaeval Studies, 1978). Notes External links Nemorarius Jordanus (1553) De ponderibus propositiones XIII - digital facsimile from the Linda Hall Library 13th-century Italian scientists Medieval European mathematics 13th-century Italian mathematicians 13th-century Latin writers 13th-century Italian writers