▁a ▁seem ingly ▁continuous ▁spectrum . ▁So on ▁after ▁this , ▁he ▁combined ▁teles cope ▁and ▁pr ism ▁to ▁observe ▁the ▁spectrum ▁of ▁Ven us , ▁the ▁Moon , ▁Mars , ▁and ▁various ▁stars ▁such ▁as ▁Bet el ge use ; ▁his ▁company ▁continued ▁to ▁manufact ure ▁and ▁sell ▁high - quality ▁ref ract ing ▁teles cop es ▁based ▁on ▁his ▁original ▁designs ▁until ▁its ▁closure ▁in ▁ 1 8 8 4 . ▁ ▁The ▁resolution ▁of ▁a ▁pr ism ▁is ▁limited ▁by ▁its ▁size ; ▁a ▁larger ▁pr ism ▁will ▁provide ▁a ▁more ▁detailed ▁spectrum , ▁but ▁the ▁increase ▁in ▁mass ▁makes ▁it ▁un su itable ▁for ▁highly ▁detailed ▁work . ▁This ▁issue ▁was ▁resolved ▁in ▁the ▁early ▁ 1 9 0 0 s ▁with ▁the ▁development ▁of ▁high - quality ▁reflection ▁grat ings ▁by ▁J . S . ▁Pl ask ett ▁at ▁the ▁Domin ion ▁Observ atory ▁in ▁Ott awa , ▁Canada . ▁Light ▁striking ▁a ▁mirror ▁will ▁reflect ▁at ▁the ▁same ▁angle , ▁however ▁a ▁small ▁portion ▁of ▁the ▁light ▁will ▁be ▁ref ract ed ▁at ▁a ▁different ▁angle ; ▁this ▁is ▁dependent ▁upon ▁the ▁indices ▁of ▁ref raction ▁of ▁the ▁materials ▁and ▁the ▁w avel ength ▁of ▁the ▁light . ▁By ▁creating ▁a ▁" bla zed " ▁gr ating ▁which ▁util izes ▁a ▁large ▁number ▁of ▁parallel ▁mirror s , ▁the ▁small ▁portion ▁of ▁light ▁can ▁be ▁focused ▁and ▁visual ized . ▁These ▁new ▁spect ro scop es ▁were ▁more ▁detailed ▁than ▁a ▁pr ism , ▁required ▁less ▁light