s ▁and ▁feelings ▁the ▁audience ▁will ▁recogn ise . ▁Special ▁effects ▁have ▁to ▁deliver ▁the ▁im itations ▁of ▁physical ▁actions ▁on ▁stage , ▁such ▁as ▁explos ions , ▁fire works , ▁fog , ▁or ▁even ▁earth qu akes ▁that ▁are ▁often ▁part ▁of ▁the ▁story . ▁R ig ging ▁is ▁an ▁important ▁aspect ▁that ▁is ▁not ▁often ▁visible . ▁All ▁sound ▁and ▁light ing ▁features ▁and ▁their ▁cab ling ▁and ▁w iring ▁have ▁to ▁be ▁held ▁in ▁a ▁safe ▁position , ▁above ▁both ▁the ▁stage ▁and ▁the ▁aud itor ium , ▁and ▁therefore ▁require ▁special ist ▁temporary ▁and ▁permanent ▁f itt ings ▁to ▁be ▁installed . ▁The ▁technical ▁director , ▁especially ▁in ▁larger ▁the at res , ▁has ▁the ▁responsibility ▁of ▁over see ing ▁the ▁rig ging ▁and ▁construction ▁of ▁the ▁stage ▁scen ery . ▁They ▁create ▁working ▁draw ings ▁from ▁the ▁scen ic ▁designer ' s ▁draw ings ▁in ▁order ▁to ▁pass ▁on ▁the ▁designs ▁to ▁the ▁scene ▁shop . ▁ ▁Tr ends ▁and ▁movements ▁ ▁The ▁three ▁un ities ▁The ▁Class ical ▁un ities ▁of ▁time , ▁action ▁and ▁place ▁were ▁the ▁main ▁principles ▁of ▁French ▁ne o - class ical ▁drama ▁during ▁part ▁of ▁the ▁ 1 7 th ▁century . They ▁were ▁introduced ▁by ▁Jean ▁Ma ire t ▁after ▁a ▁mis reading ▁of ▁Arist ot le ' s ▁Po et ics , ▁and ▁the ▁critic ▁Cast el vet ro ▁ins isted ▁that ▁play w right s ▁and ▁direct ors ▁ad here ▁to ▁the ▁un ities . ▁In ▁the ▁Po