Ontheotherhandinthecaseof（2）thePhysician，thoughIshallherealsoseealine（D’A’E’）withabrightcentre（A’），yetitwillshadeawayLESSRAPIDLYintodimness，becausethesides（A’C’，A’B’）RECEDELESSRAPIDLYINTOTHEFOG：andwhatappeartomethePhysician’sextremities，viz。D’andE’，willnotbeNOTSODIMastheextremitiesoftheMerchant。
TheReaderwillprobablyunderstandfromthesetwoinstanceshow——
afteraverylongtrainingsupplementedbyconstantexperience——
itispossibleforthewell-educatedclassesamongustodiscriminatewithfairaccuracybetweenthemiddleandlowestorders，bythesenseofsight。IfmySpacelandPatronshavegraspedthisgeneralconception，sofarastoconceivethepossibilityofitandnottorejectmyaccountasaltogetherincredible——
IshallhaveattainedallIcanreasonablyexpect。WereItoattemptfurtherdetailsIshouldonlyperplex。Yetforthesakeoftheyoungandinexperienced，whomayperchanceinfer——fromthetwosimpleinstancesIhavegivenabove，ofthemannerinwhichIshouldrecognizemyFatherandmySons——thatRecognitionbysightisaneasyaffair，itmaybeneedfultopointoutthatinactuallifemostoftheproblemsofSightRecognitionarefarmoresubtleandcomplex。