The laughter was syncopated along with the music. Serge Lang calls it a natural rhythm: 100 in a room for 30 hesitating, chuckling and then shaking, letting loose the belly laughs everyone expected.

Lang presided, patting his nose with a handkerchief and running his fingers down the chocolate strips of his velvet Renaissance doublet. Occasionally, he lip-synced to the music on his record player. Mostly, he looked around, smiling tight-lipped at what he provoked in people.

Tuesday night, Lang, a math professor and infamous rabble-rouser, gave a Pierson College Master’s Tea to a packed crowd that knew him only by reputation. It was not unusual to watch him beat his fists in the air. The crowd was there because he was doing it to Renaissance and rock music.

“This is not a troublemaking evening,” he began in a quiet voice, with a flat French “r” and a nod to the stack of records behind him.

He explained the similarities between the Elizabethan period and 1960s rock music as he might have explained what made a clutch of Yale undergraduates — with purple hair, with baseball caps and with psychology course packets — listen intently to a resident expert in diophantine geometry who is a half-century older than they are.

“The rock period lasted between ’62 and ’72 roughly,” he said from the back of his throat. “Decades like these are highly creative, spontaneous, short-lived and don’t go anywhere, like the Elizabethan period in England.”

He started with a cover of “Ding dong the Witch is Dead” done in 1969 by the Fifth Estate, followed by a piece by Michael Praetorius, which he said spent several weeks on top-10 lists in the same year but which was written in 1612. He wrote to Rolling Stone magazine to suggest they write a story about it, but they didn’t respond, he said in a dejected moment while lifting the player’s needle.

“It’s a pity,” he said. “They blew it.”

Lang punctuated every pair of old and new songs with a comment on the recording, advising potential Praetorius afficionados which recordings were successful and which were just a bunch of “musicologists doing their things.”

The first 15 minutes were golden. The little man with the nervous fingers was in his element, removing and replacing an oversized pair of tortoise shell glasses to read his set list while the audience rolled with laughter. Slowly, though, the laughter fell off beat, settling to an occasional outburst as Lang stood consumed by his soundtrack.

Few said they minded that he seemed to drift off; most were there to see the tenured professor and member of the National Academy of the Sciences do something other than launch a campaign.

“It was sheer brilliance,” said one math major who declined to give his name for fear of Lang’s response. “It’s not as unusual as would be expected from Serge Lang.”

“It’s too bad he didn’t bring his lute,” said the psychology major next to him, also afraid to give her name.

But it is for the campaigns, not the musical instruments, that most knew him.

In 1987, Lang launched one to keep a famous Harvard social scientist from being accepted into the Academy. The New York Times reported at the time that Lang supplied a “ton of evidence” to the thousands of members to convince them to reject Samuel P. Huntington, director of Harvard’s Center for International Studies at the time. It was his great success in problem-causing.

At Yale, the holder of a Princeton doctorate composed the “Teaching and Learning File,” a more than 200 page collection of letters in opposition to and in response to his opposition to a 1985 speech on Marxism given at Yale by Jon Wiener, a contributing writer for The Nation. His more recent work has included articles disputing the link between HIV and AIDS.

But on Tuesday night, Lang bobbed his head to pacifists’ songs and mouthed the Beatles’ “Try to See it My Way.” He looked pleased when people jeered medieval music, pleased when they asked for an encore when he was wrapping up at 9 p.m., cinched-mouth and smiling even when people left before he got a chance to punctuate his last song.

As the back of the crowd filed out, he lifted the needle on a Renaissance record and with his back half-turned from his fans, said, “Well that, ladies and gentlemen, is it.”

[ydn-legacy-photo-inline id=”20220″ ]