In particular when three comets appeared in 1618 he became involved in a controversy regarding the nature of comets. He argued that they were close to the Earth and caused by optical refraction.
Sa mga partikular na kapag tatlong comets ay lumitaw sa 1618 siya ay naging kasangkot sa isang pagtatalo tungkol sa kalikasan ng comets. He argued na sila ay malapit na ang Earth at sanhi ng mata repraksyon.