subsequently, milanković wrote the introductory portion of "mathematical science of climate and astronomical theory of the variations of the climate" ("mathematische klimalehre und astronomische theorie der klimaschwankungen"), published by köppen ("handbook of climatology"; "handbuch der klimalogie band 1") in 1930 in german and translated into russian in 1939. in 1934 milanković published the book "celestial mechanics". this textbook used vector calculus systematically to solve problems of celestial mechanics.