 Meyerbeer was always concerned to intensify the theatricality of his operas , even when new ideas emerged at a relatively late stage in the music 's composition . An example of his <unk> was the addition of the provocative " Ballet of the Nuns " in the third act of Robert le diable , at the suggestion of Duponchel . The set for the ballet was an innovative and striking design by Duponchel and Pierre @-@ Luc @-@ Charles <unk> . Duponchel had also introduced technical innovations for the staging , including ' English traps ' for the sudden appearance and disappearance of the ghosts . ( Meyerbeer was led in fact to complain that the spectacle was too much and was pushing his music into the background ) . In Le prophète the skating ballet , which created a great sensation , was composed after rehearsals had begun , in order to <unk> on the new craze for roller <unk> . The theatre was also able to use new electrical lighting effects to create a powerful <unk> , and to depict the <unk> which ends the opera . 
