7:30
By 7:30 o'clock in the evening the Central Hall was packed to the walls , no reserved seats were sold , and the rule was observed `` First come , first served , '' which brought promptly the audience . Season ticket-holders had the exclusive right to the hall till 7:25 o'clock , when a limited number of single admission tickets were sold . A large force of polite ushers assisted in seating the people , and in keeping order . At 7:30 all the entrance doors were closed , so that late comers never disturbed the audience . The musical prelude , or orchestra concert of thirty minutes closed at 7:30 with a grand chorus by the audience standing ; following this , precisely at 7:30 was the half-hour lecture-prelude on some scientific or practical subject . Among the topics treated were `` Wrongs of Workingmen , and How to Right Them , '' `` The Terminal Glacier , '' `` Sewerage and Ventilation , '' `` The Pyramids , '' `` Wonders of the House we Live in , '' `` Architecture Illustrated , '' etc. . From 8:00 to 8:15 followed the popular Singing School , in which five thousand persons heartily joined , aided by an enthusiastic precentor , and orchestra , in singing national hymns and other music .