A poet, environmentalist, instrument builder, musicologist, calligrapher and political activist. Lou Harrison, born 100 years ago in Portland, Ore., was all these things.

Above all, though, he was a composer. And his centenary is celebrated this week with a festival staged by Zeitgeist, the contemporary music group based in St. Paul’s Lowertown.

Thursday evening’s opening concert was a lovingly crafted taster menu of Harrison’s fabulously varied chamber music. It began, fittingly, with the ululating sounds of a solitary oboe — like a muezzin calling the faithful to prayer — in “Music for Remy.”

The evocative, Middle Eastern ambience of the piece is no accident. Harrison had a passion for what we now call world music, and was a pioneer of incorporating non-Western music into his own compositions.

Harrison’s particular fascination with the Indonesian gamelan — an orchestra of tuned percussion instruments made of bamboo, wood and metal — was well represented, especially in “Varied Trio” for piano, violin and percussion.

The “percussion” in question is anything but the standard classical complement of drums, timpani and cymbals. Rather, eight rice bowls were tuned by partial fills of water and played with chopsticks. They twinkled busily in the trio’s second movement to a snappy accompaniment of violin pizzicati.

And then, for the same piece, six baking pans of varying sizes were beaten with a drumstick while the piano’s strings were plucked manually and the instrument’s outer casing was hit with a small mallet.

Perhaps it all sounds gimmicky, but it isn’t. Harrison was a master of inventing new sonorities and using them for the betterment of his material, not for superficial decoration.

He also was unafraid to write melodies you can whistle — at a time when gnarled complexity and furrow-browed intensity were more fashionable than pleasing audiences.

The whimsical “New York Waltzes” played by pianist Nikki Melville showed Harrison’s natural gift for a beguiling melody. So, too, did the softly melancholic “Songs in the Forest” for flute, violin, piano and percussion, where Harrison evokes the beauty and mystery of the natural world with a vernal clarity of vision.

The performances by Zeitgeist were uniformly excellent and sympathetically attuned to the warmth, wit and humanity of Harrison’s uniquely companionable music.

Above all, they captured the sense of childlike play in Harrison’s music — the visceral joy he took in sound and in exploring new combinations of timbre.

The two remaining concerts in Zeitgeist’s Harrison festival examine his music for voice, gamelan and percussion. They are a must for anyone interested in this true American original. Or for anyone who thinks music can be a genuinely life-enhancing experience.

Terry Blain writes about classical music and theater.