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The observatory sits at the tip of Ö�����Ի�, an island in the Baltic Sea about 300 kilometers as the wigeon flies from the park in Germany where the white-tailed eagles reside.

As Oland turned its handle, the machine spun out a roll of paper punched with the swirling piano line — seeming to repeat itself but, in its small changes, irresistibly moving.

But it was less so on Thursday as the Danes — Norgaard, as well as the violinists Frederik Oland and Rune Tonsgaard Sorensen, and the cellist Fredrik Schoyen Sjolin — skipped the written reprises of the first two movements’ opening sections.

For the three Danes who met as not-yet-teenagers — the violinists Frederik Oland and Rune Tonsgaard Sorensen and the violist Asbjorn Norgaard — and the Norwegian cellist Fredrik Schoyen Sjolin, who joined them in their 20s, music has long been an act of friendship.

When I was growing up, television stations still occasionally broadcast the old Charlie Chan movies from the 1930s, which starred a Swedish actor, Warner Oland, as a Chinese American detective.