▁two ▁equ ino xes , ▁in ▁contrast ▁to ▁the ▁older ▁Chal de an ▁( B ab yl onian ) ▁system , ▁which ▁placed ▁these ▁points ▁within ▁the ▁z od iac ▁signs . ▁This ▁illustr ates ▁that ▁P to le my ▁merely ▁clar ified ▁the ▁convention ▁of ▁Greek ▁astronom ers ▁and ▁did ▁not ▁origin ate ▁the ▁principle ▁of ▁the ▁tropical ▁z od iac , ▁as ▁is ▁sometimes ▁assumed . ▁ ▁P to le my ▁also ▁demonstr ates ▁that ▁the ▁principle ▁of ▁the ▁tropical ▁z od iac ▁was ▁well ▁known ▁to ▁his ▁prede cess ors ▁within ▁his ▁ast ro log ical ▁text , ▁the ▁T et rab ib los , ▁where ▁he ▁explains ▁why ▁it ▁would ▁be ▁an ▁error ▁to ▁associate ▁the ▁regularly ▁spac ed ▁signs ▁of ▁the ▁season ally ▁aligned ▁z od iac ▁with ▁the ▁irregular ▁boundaries ▁of ▁the ▁visible ▁const ell ations : ▁ ▁The ▁beg inn ings ▁of ▁the ▁signs , ▁and ▁like wise ▁those ▁of ▁the ▁terms , ▁are ▁to ▁be ▁taken ▁from ▁the ▁equ ino ct ial ▁and ▁tropical ▁points . ▁This ▁rule ▁is ▁not ▁only ▁clearly ▁stated ▁by ▁writers ▁on ▁the ▁subject , ▁but ▁is ▁also ▁especially ▁evident ▁by ▁the ▁demonstr ation ▁constantly ▁afford ed , ▁that ▁their ▁n atures , ▁influ ences ▁and ▁familiar ities ▁have ▁no ▁other ▁origin ▁than ▁from ▁the ▁trop ics ▁and ▁equ ino xes , ▁as ▁has ▁been ▁already ▁plain ly ▁shown . ▁And , ▁if ▁other ▁beg inn ings ▁were ▁allowed , ▁it ▁would ▁either ▁be ▁necessary ▁to ▁exclude ▁the ▁n atures ▁of