He also wrote other works about geometry or geodesy .
Graf 's mathematical work focuses on the Bessel functions , a topic about he published a book with Salomon Eduard Gubler , published in two volumes appeared in 1898 and 1900 .
Graf also wrote other works about geometry or geodesy .
Graf 's mathematical work focuses on the Bessel functions , a topic about he published a book with Salomon Eduard Gubler , published in two volumes appeared in 1898 and 1900 .