There’s never a good time for a busy orchestra conductor to fall ill. But for Seattle Symphony Music Director Thomas Dausgaard and regional music lovers, the indisposition that kept him off the podium for this week’s concerts is particularly unfortunate.

Not only had Dausgaard just fought his way past visa restrictions to Seattle (from his native Denmark) for last week’s concerts; this week’s Thursday/Saturday program posed some considerable challenges for a replacement maestro. The concert lineup, featuring two major works by women composers, is not in every conductor’s repertoire. The program’s centerpiece is the world premiere of a genuine rarity: a double harp concerto, commissioned by the Seattle Symphony, with the composer Hannah Lash as one of the two soloists. And the other work on the program, the 1894 “Gaelic” Symphony of Amy Beach, is performed seldom enough that its appearance is a notable event.

Fortunately, the orchestra’s associate conductor, Lee Mills, was at hand as Dausgaard’s substitute, and he proved the hero of the hour. Just keeping the full orchestra and the two harp soloists together in the world premiere of the complicated 35-minute, four-movement “The Peril of Dreams” was quite a feat. Mills, who clearly knew the score, did considerably more than direct traffic; he brought out the subtle textures and balances of the music.

The new concerto is a work of considerable beauty, with delicate, feathery glissandi in the two harps, a bewitching double cadenza, and intricate rhythmic patterns. Mills supported the brilliant solo harpists (the composer, and the orchestra’s own Valerie Muzzolini) and let them shine.

Lash, who turns 40 next week, is a remarkably multifaceted musician: a pianist as well as a composer and harpist. She holds postgraduate degrees from Harvard, Yale and the Cleveland Institute of Music, and is now a professor at Mannes School of Music. It’s a life that would have been unimaginable to Amy Beach (1867-1944), a gifted pianist and composer who (during her husband’s lifetime) was referred to as “Mrs. H.H.A. Beach.”

Her “Gaelic” Symphony, incorporating folk themes from her background in the British Isles, is a work of considerable charm, and it got a rousing, high-energy performance from Mills and the orchestra on Thursday evening. With its abundance of melodies, the “Gaelic” Symphony offered great solo opportunities to the orchestra’s principals, particularly the winds, who outdid themselves in this spirited score.

Beach “Gaelic” Symphony, Lash “The Peril of Dreams”

Seattle Symphony, with Lee Mills conducting, and harp soloists Hannah Lash and Valerie Muzzolini; Benaroya Hall, Thursday evening (repeated at 8 p.m. Saturday, Nov. 20; $24-$129). Thursday’s performance will also be livestreamed on the subscription-only Seattle Symphony Live, viewable for a week after initial airdate. 206-215-4747,