▁crossed ▁w ires ▁at ▁the ▁foc al ▁point ▁to ▁define ▁the ▁centre ▁of ▁the ▁field ▁of ▁view . ▁He ▁then ▁added ▁this ▁arrangement ▁to ▁a ▁se xt ant ▁model led ▁on ▁the ▁instrument ▁used ▁by ▁Ty cho ▁Bra he , ▁although ▁Ty cho ’ s ▁se xt ant ▁was ▁only ▁a ▁n aked - ey e ▁instrument . ▁Gas co igne ' s ▁se xt ant ▁was ▁five ▁feet ▁in ▁radius , ▁and ▁measured ▁the ▁distance ▁between ▁astronom ical ▁bodies ▁to ▁an ▁un pre ced ented ▁degree ▁of ▁accuracy . ▁Gas co igne ▁then ▁real ised ▁that ▁by ▁introdu cing ▁two ▁points , ▁whose ▁separation ▁could ▁be ▁adjust ed ▁using ▁a ▁sc rew , ▁he ▁could ▁measure ▁the ▁size ▁of ▁the ▁image ▁en closed ▁by ▁them . ▁Using ▁the ▁known ▁pitch ▁of ▁the ▁sc rew , ▁and ▁knowing ▁the ▁foc al ▁length ▁of ▁the ▁l ens ▁producing ▁the ▁image , ▁he ▁could ▁work ▁out ▁the ▁size ▁of ▁the ▁object , ▁such ▁as ▁the ▁Moon ▁or ▁the ▁plan ets , ▁to ▁a ▁h ither to ▁un att ain able ▁degree ▁of ▁accuracy . ▁ ▁Gas co igne ▁met ▁the ▁Lanc ash ire ▁astronom er ▁William ▁Cra bt ree , ▁probably ▁in ▁ 1 6 4 0 . ▁After ▁making ▁observations ▁at ▁Gas co igne ' s ▁home , ▁Cra bt ree ▁was ▁much ▁taken ▁with ▁these ▁invent ions ▁and ▁immediately ▁saw ▁their ▁significance . ▁On ▁his ▁return ▁to ▁his ▁home ▁in ▁Br ought on , ▁just ▁outside ▁Manchester , ▁he ▁wrote ▁to ▁Gas co