Dactyliology – study of rings Dactylography – study of fingerprints Dactylology – study of sign language Deltiology – collection and study of picture postcards Demography – study of population Demology – study of human behaviour Demonology – study of demons Dendrochronology – study of tree rings Dendrology – study of trees Deontology – theory or study of moral obligation Dermatoglyphics – study of skin patterns and fingerprints Dermatology – study of skin Desmology – study of ligaments Diabology – study of devils Diagraphics – art of making diagrams or drawings Dialectology – study of dialects Dioptrics – study of light refraction Diplomatics – science of deciphering ancient writings and texts Diplomatology – study of diplomats Docimology – art of assaying Dosiology – study of doses Dramaturgy – art of producing and staging dramatic works Dysgenics – study of racial degeneration Dysteleology – study of purposeless organs