Leonardo certainly was in relation with some persons belonging to that circle when he published in 1220 another more extensive work, De practica geometriae, which he dedicated to the imperial astronomer Dominicus Hispanus.
The other works consist of the Practica geometriae and some most striking papers of the greatest scientific importance, amongst which the Liber quadratorum may be specially signalized.
In his Practica geometriae plain traces of the use of the Roman agrimensores are met with; in his Liber abaci old Egyptian problems reveal their origin by the reappearance of the very numbers in which the problem is given, though one cannot guess through what channel they came to Leonardo's knowledge.
The second work of Leonardo, his Practica geometriae (1220) requires readers already acquainted with Euclid's planimetry, who are able to follow rigorous demonstrations and feel the necessity for them.
Among the writers it may be sufficient to mention here Gariopontus; Copho, who wrote the Anatome porci, a well-known medieval book; Joannes Platearius, first of a family of physicians bearing the same name, whose Practica, or medical compendium, was afterwards several times printed; and Trotula, believed to be the wife of the last-named.
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