of the Mahavishnu Orchestra or Chick Corea's density.

Their gains have been more palpable, though, especially since jazz rock has grown lazy. Jaco Pastorius, the bassist who joined them on their last album, has been instrumental in developing their busier, talkative style. He coproduced Heavy Weather and his two compositions are the strongest.

"Havona" is a rollicking number with most of the soloing by Pastorius. It builds slowly from Zawinul's opening chords to a brief solo by Shorter on soprano; from there Pastorius leads the way to the cut's strong conclusion, a thundering double-time drone from all the players.

Zawinul's best contribution is the opening cut, "Birdland." His synthesizer playing, warm and bluesier than usual, sounds like a guitar in spots. After a playful opening, a more-than-danceable melody takes over, filled and given dimension by Shorter's sax, but again anchored by Pastorius.

Pastorius has been recording frequently with other people of late, so how long he'll remain in Weather Report is anybody's guess. He's vital to them now because he fills up the music where it used to diffuse, which suits their apparent aims just fine. There was a time when Weather Report's music went up and up only; becoming more ethereal as it went; the new bottom makes all the difference in the world. (RS 242)

DAN OPPENHEIMER