He mea nui ki a Rasmus Bartholin tōna kitenga (1669) o te whakahekenga rua o te hihi mā te Iceland spar (calcite). I whakaputaina e ia tētahi whakaahuatanga tika o te āhuatanga, engari i te mea i mārama kētia te āhua ōkiko o te marama i taua wā, kāore i taea e ia te whakamārama. I muri noa iho i te whakatakoto a Thomas Young i te ariā ngaru o te marama, i te tau 1801 ka taea te whakamārama. Pātai: He aha i kore ai a Rasmus e whakamārama i te āhuatanga?
i mārama iti te āhua ōkiko o te marama i taua wa