The source of the subtitle, "Jupiter," traditionally associated with Mozart's great last symphony, is not known. At any rate, the composer was not responsible for it. Mozart truly did "launch his lightning" in the summer of 1788 when he composed his trilogy of final symphonies in the fantastically brief period of about six weeks. The world would know nothing today about a Haffner family of Salzburg - rich bankers and merchants - if Mozart had not composed two delightful instrumental works to their order. The coupling of these two masterpieces enables US to note the extent to which Mozart matured during the six years intervening between their dates of composition; and William Steinberg and the Pittsburgh Symphony highlight the best in both works in brilliantly penetrating interpretations.