▁received ▁his ▁Ph D ▁in ▁ 1 8 9 8 ▁with ▁his ▁th esis ▁published ▁in ▁the ▁Ast ro phys ical ▁Journal , ▁which ▁included ▁a ▁discussion ▁of ▁the ▁amount ▁of ▁ast ig mat ism ▁of ▁a ▁con ca ve ▁gr ating . ▁While ▁at ▁Hop kins , ▁his ▁astronom y ▁duties ▁consisted ▁of ▁car ing ▁for ▁the ▁astronom ical ▁trans it ▁instrument ▁and ▁the ▁clock s ▁in ▁the ▁little ▁observ atory ▁behind ▁the ▁physics ▁labor atory , ▁and ▁the ▁ 9 . 5 - inch ▁ref ractor ▁in ▁the ▁d ome ▁of ▁the ▁labor atory ▁roof . ▁ ▁Y erk es ▁Observ atory ▁Following ▁rece ipt ▁of ▁his ▁doctor al ▁degree , ▁Mitchell ▁set ▁out ▁for ▁the ▁brand ▁new ▁Y erk es ▁Observ atory ▁in ▁Wisconsin ▁where ▁he ▁began ▁work ▁as ▁a ▁research ▁student ▁in ▁ 1 8 9 8 . ▁Though ▁he ▁enjoyed ▁his ▁work ▁at ▁Y erk es , ▁he ▁was ▁ent iced ▁to ▁move ▁away ▁and ▁became ▁an ▁instruct or ▁in ▁astronom y ▁at ▁Columbia ▁University ▁in ▁June ▁ 1 8 9 9 . ▁Over ▁the ▁four teen ▁years ▁he ▁was ▁at ▁Columbia , ▁Mitchell ▁taught ▁under grad uate ▁courses ▁in ▁descript ive ▁astronom y ▁both ▁at ▁Columbia ▁and ▁later ▁for ▁girls ▁from ▁Bar n ard ▁College , ▁a ▁year ▁long ▁course ▁in ▁ge odes y ▁for ▁third ▁year ▁students , ▁which ▁continued ▁into ▁a ▁first ▁sem ester ▁fourth ▁year ▁course , ▁and ▁a ▁six - week ▁summer ▁camp ▁for ▁civil ▁engine ers . ▁ ▁Eclipse ▁work ▁In ▁