 This particular concert was originally a two episode broadcast, as were all  of the Toscanini NBC Symphony radio broadcasts of operas. Acts I and II of  "Aida" were broadcast as Part I of the opera, and Acts III and IV were  broadcast one week later, as Part II. Toscaninis programs usually ran no  more than an hour or an hour and five minutes. For broadcasts of Beethovens  Ninth Symphony, and for his NBC Symphony opera broadcasts the hour was  lengthened by only fifteen minutes, so all of the operas had to be broadcast  in two separate installments.