Joannes della Faille s.j. Mathematics, Modesty and Missed Opportunities

Every study on sir Anthony Van Dijck contains the portrait of Joannes della Faille s.j. While the portrait is well-known, much less is known about the sitter. Yet Joannes della Faille (1597-1652) was one of the finest mathematicians of his generation. He was one of the first students of Gregorius a Sancto Vincentio s.j. and arguably his best. Della Faille published only one book ‘De Centro Gravitatis’ in which he calculates the centroid of an ellipse sector. Although this book is elegantly written it was soon superseded by other books on the same subject. This means that della Faille became no more than a footnote in the history of mathematics. Newly discovered manuscript evidence shows that della Faille’s research on conic sections was probably on par with that of Pascal and Desargues, whose mathematical work was only saved from oblivion in the nineteenth century. Della Faille did not have that luck and consequently was nearly forgotten. In this study della Faille’s results are discussed and a plea is made for reappraisal of his work.