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           But,inasmuchasitisequallynecessarytotakeintoaccountthedeviationwhichtherotarymotionoftheearthwillimparttotheshot,andastheshotcannotreachthemoonuntilafteradeviationequalto16radiioftheearth,which,calculateduponthemoon’sorbit,areequaltoaboutelevendegrees,itbecomesnecessarytoaddtheseelevendegreestothosewhichexpresstheretardationofthemoonjustmentioned:thatistosay,inroundnumbers,aboutsixty-fourdegrees.Consequently,atthemomentoffiringthevisualradiusappliedtothemoonwilldescribe,withtheverticallineoftheplace,anangleofsixty-fourdegrees.

           TheseareouranswerstothequestionsproposedtotheObservatoryofCambridgebythemembersoftheGunClub:

           Tosumup—

           1st.Thecannonoughttobeplantedinacountrysituatedbetween0°and28°ofN.orS.lat.

           2nd.Itoughttobepointeddirectlytowardthezenithoftheplace.

           3rd.Theprojectileoughttobepropelledwithaninitialvelocityof12,000yardspersecond.

           4th.Itoughttobedischargedat10hrs.46m.40sec.ofthe1stofDecemberoftheensuingyear.

           5th.Itwillmeetthemoonfourdaysafteritsdischarge,preciselyatmidnightonthe4thofDecember,atthemomentofitstransitacrossthezenith