Without a title, it's difficult to tell you where to find the poem. I did a search for Lowell's poems that contain the words "hand" and "opera" and found "An Opera House." Could this be the poem you want? Here are a few lines:

The opera house is a treasure-box of gold.
Gold in a broad smear across the orchestra pit:
Gold of horns, trumpets, tubas;
Gold -- spun-gold, twittering-gold, snapping-gold
Of harps.
The conductor raises his baton,
The brass blares out
Crass, crude,
Parvenu, fat, powerful,
Golden.
Rich as the fat, clapping hands in the boxes.
Cymbals, gigantic, coin-shaped,
Crash.

I've added to the sources section links to a couple of web sites where you can read the entire poem. I hope this helps!